Vascular prostheses for treating aneurysms

ABSTRACT

An endovascular sealing stent-graft is configured to initially be positioned in a delivery catheter in a radially-compressed state, and to assume a radially-expanded state upon being deployed from the delivery catheter. The stent-graft includes a structural member, which includes a plurality of structural stent elements, and which, when the stent-graft assumes the radially-expanded state, has a generally tubular shape, and is shaped so as to define at least two elongated indentations, each of which extends rostrally to a rostral end of the structural member, and is tapered in a caudal direction until the indentation converges with the generally tubular shape of the structural member, and each of which has an axial length of at least 2 cm. The stent-graft further includes a fluid flow guide, which is coupled to at least a portion of the structural member, and covers at least a portion of each of the elongated indentations.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/IB2010/052861, filed on Jun. 23, 2010, which claims priority fromU.S. Provisional Patent Application Nos. 61/219,758, filed on Jun. 23,2009 and 61/221,074, filed on Jun. 28, 2009, the contents of all ofwhich are incorporated herein by reference in their entirety.

FIELD OF THE APPLICATION

This present application relates generally to prostheses and surgicalmethods, and specifically to tubular prostheses, including endovasculargrafts and stent-grafts, and surgical techniques for using theprostheses to maintain patency of body passages such as blood vessels,and treating aneurysms.

BACKGROUND OF THE APPLICATION

Endovascular prostheses are sometimes used to treat aortic aneurysms.Such treatment includes implanting a stent or stent-graft within thediseased vessel to bypass the anomaly. An aneurysm is a sac formed bythe dilation of the wall of the artery. Aneurysms may be congenital, butare usually caused by disease or, occasionally, by trauma. Aorticaneurysms which commonly form between the renal arteries and the iliacarteries are referred to as abdominal aortic aneurysms (“AAAs”). Otheraneurysms occur in the aorta, such as thoracic aortic aneurysms (“TAAs”)and aortic uni-iliac (“AUI”) aneurysms.

“Endoleak” is the persistent flow of blood into the aneurismal sac afterimplantation of an endovascular prosthesis. The management of some typesof endoleak remains controversial, although most can be successfullyoccluded with surgery, further stent implantation, or embolization. Fourtypes of endoleaks have been defined, based upon their proposedetiology, as described below.

A type I endoleak, which occurs in up to 10 percent of endovascularaortic aneurysm repairs, is due to an incompetent seal at either theproximal or distal attachment sites of the vascular prosthesis,resulting in blood flow at the end of the prosthesis into the aneurismalsac. Etiologies include undersizing of the diameter of the endograft atthe attachment site and ineffective attachment to a vessel wall that isheavily calcified or surrounded by thick thrombus. Type I failures havealso been found to be caused by a continual expansion of the aneurysmneck (the portion of the aorta extending cephalad or caudad from theaneurysm, and is not dilated). This expansion rate has been estimated tobe about one millimeter per year. Because the aneurysm neck expandsbeyond the natural resting diameter of the prosthesis, one or morepassageways are defined about the prosthesis in communication with theaneurismal sac. Additionally, Type I endoleaks may be caused whencircular prostheses are implanted in non-circular aortic lumens, whichmay be caused by irregular vessel formation and/or calcified topographyof the lumen of the aorta.

Type I endoleaks may occur immediately after placement of theprosthesis, or may be delayed. A delayed type I endoleak may be seenduring follow-up studies if the prosthesis is deployed into a diseasedsegment of aorta that dilates over time, leading to a breach in the sealat the attachment site.

Type I endoleaks must be repaired as soon as they are discovered,because the aneurismal sac remains exposed to systemic pressure,predisposing to aneurysmal rupture, and spontaneous closure of the leakis rare. If discovered at the time of initial placement, repair mayconsist of reversal of anticoagulation and reinflation of the deploymentballoon for an extended period of time. These leaks may also be repairedwith small extension grafts that are placed over the affected end. Thesemethods are usually sufficient to exclude the aneurysm. Conversion to anopen surgical repair may be needed in the rare situation in which theleak is refractory to percutaneous treatment.

Type II endoleaks are the most prevalent type, occurring in 10 to 25percent of endovascular aortic aneurysm repairs, and are characterizedby flow into and out of the aneurismal sac from patent branch vessels.These endoleaks are most often identified on the post procedural CT, inwhich these leaks appear as collections of contrast outside of theendograft, but within the aneurismal sac. The most frequent sources oftype II endoleaks are collateral backflow through patent lumbar arteriesand a patent inferior mesenteric artery. Because the sac fills through acollateral network, the endoleak may not be visualized on the arterialphase of CT scanning; delayed imaging is thus required.

Type III and type IV endoleaks are much less common. Type III endoleaksrepresent flow into the aneurismal sac from separation betweencomponents of a modular system, or tears in the endograft fabric. TypeIV endoleaks are due to egress of blood through the pores in the fabric.Type IV leaks heal spontaneously, while type III leaks are repaired withan additional endograft to eliminate systemic flow and pressure in theaneurysm.

As can be readily appreciated, even with the successful implantation ofan endovascular prosthesis, failures may occur thereafter. It has beenfound that type I failures may affect up to 5-10% of all implantedprostheses. Accordingly, there is a clear need for an endovascularprosthesis which can reduce the likelihood of, and ideally eliminate,type I failures.

U.S. Pat. No. 7,044,962 to Elliott describes an implantable prosthesiswith a radially-expandable tubular body and at least one skirt extendingtherefrom. The skirt in his invention terminates in a peripheral edge.At least portions of the peripheral edge are free and displaceable to agreater diameter of the tubular body. Thus, with the implantableprosthesis being a stent-graft used to treat an aortic aneurysm (e.g.,AAA), the skirt may be used to inhibit type I endoleaks upon itsselective displacement in response to irregular aortic shaping and/oraneurysm neck expansion. The skirt may actively inhibit type I endoleaksby forming a physical barrier against flow between the tubular body andthe aortic wall. In addition, the skirt may passively inhibit endoleakformation by sufficiently restricting blood flow to allow coagulationand clot formation, which would act as a barrier against endoleakage.

U.S. Pat. No. 4,938,740 to Melbin describes a technique in whichdiseased portions of a blood vessel, such as with an aneurysm, areablated and replaced with a prosthetic member. This technique, however,requires open surgery. As an improvement over this technique,endovascular emplacement techniques have been developed to implantgrafts and stent-grafts into a vessel from a remote puncture site,thereby obviating the need for open surgery. For example, anendovascular prosthesis (stent or stent-graft) is positioned to bypassthe aneurysm with the ends of the prosthesis being in contiguous contactwith healthy portions of the aorta, the prosthesis having beenintroduced endovascularly (e.g., with a catheter). Accordingly, if theaneurysm were to rupture, blood flow through the aorta would beuninterrupted, and internal bleeding generally avoided.

PCT Publication WO 2008/107885 to Shalev et al., and US PatentApplication Publication 2010/0063575 to Shalev et al. in the US nationalstage thereof, which are incorporated herein by reference, describe amultiple-component expandable endoluminal system for treating a lesionat a bifurcation, including a self expandable tubular root member havinga side-looking engagement aperture, and a self expandable tubular trunkmember comprising a substantially blood impervious polymeric linersecured therealong. Both have a radially-compressed state adapted forpercutaneous intraluminal delivery and a radially-expanded state adaptedfor endoluminal support.

The following references may be of interest:

-   U.S. Pat. No. 5,824,040 to Cox et al.-   US Patent Application Publication 2006/0229709 to Morris et al.-   US Patent Application Publication 2006/0241740 to Vardi et al.-   US Patent Application Publication 2008/0109066 to Quinn

SUMMARY

Some applications of the present invention provide an endovascularstent-graft, which comprises a structural member and a fluid flow guide.When the stent-graft assumes a radially-expanded state upon beingdeployed from a delivery catheter, the fluid flow guide is shaped so asto define radially-diverging and radially-converging portions, whichtogether define a bulge that extends radially outward. When thestent-graft is deployed in an aneurysmatic abdominal aorta, the bulgeextends radially outward against a rostral portion of the aorticaneurysm, thereby helping prevent a current or a future type I endoleak.

Typically, the stent-graft is configured such that the bulge expandsradially as the rostral end of the aneurysm enlarges, in order tomaintain a tight seal with the wall of the aorta, thereby preventingcurrent or future type I endoleaks. At the same time, the stent-graft isconfigured to apply a radially-outward force that is sufficient to causethe bulge to expand with the aortic wall, but insufficient to itselfcause expansion of the aortic wall. The crossing profile of thestent-graft when it assumes a radially-compressed state is less than thecrossing profile would be if the bulge were instead provided by aseparate skirt. Use of a separate skirt would necessitate additional,overlapping material of the fluid flow guide, and additional structuralstent elements.

For some applications, a rostral-most first portion of the structuralmember defines a plurality of anchoring elements that extend radiallyoutwardly, and, optionally, rostrally, when the stent-graft assumes theradially-expanded state. The anchoring elements anchor the stent-graftto the vascular wall, helping prevent dislodgement. A second portion ofthe structural member defines a stent body when the stent-graft assumesthe radially-expanded state.

In some applications of the present invention, an endovascularstent-graft comprises a foldable skirt. The stent-graft comprises astructural member, a fluid flow guide, a rostrally-positioned foldableskirt. A rostral-most first portion of the structural member defines aplurality of anchoring elements that extend radially outwardly androstrally when the stent-graft assumes the radially-expanded state. Asecond portion of the structural member defines a tubular body when thestent-graft assumes the radially-expanded state. The skirt extends fromthe structural member at a circumferential juncture between theanchoring elements and the tubular body, and terminates in a peripheraledge. The peripheral edge has a greater circumference than that of thecircumferential juncture when the stent-graft assumes theradially-expanded state.

The skirt extends rostrally from the circumferential juncture, radiallysurrounding the anchoring elements, when the stent-graft is initiallypositioned in a delivery catheter, and retains this position initiallyupon being deployed from the catheter. This rostrally-extending positionfacilitates low-profile mounting of the endovascular stent-graft in theradially-compressed state within the delivery catheter. Upon applicationof a caudally-directed force to the peripheral edge of the skirt afterdeployment of the stent-graft from the delivery catheter, the skirtextends caudally from the circumferential juncture, in order tofacilitate sealing of blood leakage around the stent-graft.

In some application of the present invention, an endovascular prosthesiscomprises a structural member, which in part defines a stent body; aplurality of circumferentially disposed tissue engagement members; and aplurality of communicating members that respectively connect thestructural member to the tissue engagement members. For someapplications, the prosthesis further comprises a fluid flow guide. Thetissue engagement members are disposed externally to the stent body whenthe prosthesis assumes the radially-expanded state. The communicatingmembers are generally radially-oriented when the prosthesis assumes theradially-expanded state. Typically, the tissue engagement members areblunt. As a result, the tissue engagement members cause low trauma tothe wall of the aorta, and typically do not pierce the wall. Typically,several weeks after placement of the prosthesis, the tissue engagementmembers become embedded in the wall of the aorta, thereby helping holdthe prosthesis in place. Typically, each of the tissue engagementmembers extends in one or more directions generally parallel to asurface of the stent body.

For some applications, the tissue engagement members are generallycircumferentially arcuate and extend laterally around the stent body.For other applications, the tissue engagement members are generallylinear and extend axially along the stent body. For still otherapplications, the tissue engagement members are polygonal, e.g.,diamond-shaped, similar to the shape of standard stent closed cells.

In some applications of the present invention, a doubly-flaredendovascular stent-graft prosthesis comprises a structural member. Whenthe prosthesis assumes a radially-expanded state, the structural memberis shaped so as to define: (a) a flared rostral portion, which flaresradially outward in a rostral direction, (b) a flared caudal portion,which flares radially outward in a caudal direction, and, optionally,(c) a generally constant-diameter body portion, which is disposedlongitudinally between the flared rostral and caudal portions.

For some applications, a spring coefficient of the flared caudal portionis (a) at least 20% less than a spring coefficient of the body portion,and/or (b) at least 20% less than a spring coefficient of the flaredrostral portion. The low spring coefficient helps the flared caudalportion to maintain a tight seal with the wall of the aorta, therebypreventing current or future type I endoleaks. At the same time, flaredcaudal portion is configured to apply a radially-outward force that issufficient to expand with the aortic wall, but insufficient to itselfcause expansion of the aortic wall.

For some applications, the prosthesis further comprises astent-engagement member, which, when the prosthesis assumes theradially-expanded state, is generally tubular. The stent-engagementmember is configured to be sealingly coupled to a primary stent-graft.The stent-engagement member is disposed at least partially within atleast one portion selected from the group consisting of: the flaredcaudal portion, and the body portion. Typically, the prosthesis furthercomprises a biologically-compatible substantially fluid-imperviousflexible sheet, which at least partially covers the stent-engagementmember.

The prosthesis is typically transvascularly introduced into the aorta,and positioned such that the flared caudal portion is disposed inrostral end of an abdominal aortic aneurysm. The flare of the caudalportion seals the prosthesis to the rostral end of the aneurysm, therebyreducing a current or future risk for type I endoleak.

In some applications of the present invention, a self-expandinglumen-engagement prosthesis member, which is generally tubular when theprosthesis member assumes a radially-expanded state, comprises aplurality of support members distributed around a circumference of theprosthesis member. The support members are shaped so as to definerespective curves having concavities that face radially outward. Theprosthesis member further comprises a plurality of rostral barbs and aplurality of caudal barbs, disposed more caudally than the rostralbarbs. When the prosthesis member assumes the radially-expanded state,the rostral barbs extend caudally and radially outwardly from respectiveones of support members, and the caudal barbs extend rostrally andradially outward from respective ones of the support members. Therostral barbs are typically only slightly caudally oriented, and thecaudal barbs are typically only slightly rostrally oriented. Typically,the rostral and caudal barbs are disposed at rostral and caudal ends ofthe support members, respectively.

The oppositely-oriented rostral and caudal barbs axially pinch tissue ofthe aorta between the barbs, thereby anchoring the prosthesis member tothe aorta. The concavity of the support members generally increases theaxial forces applied by the barbs. For some applications, the prosthesismember is configured to longitudinally shorten as the prosthesis membertransitions from a radially-compressed state to the radially-expandedstate, thereby bringing the rostral and caudal ends of the supportmembers closer to each other, as an average diameter of the structuralmember increases. For some applications, the prosthesis member ismounted at a rostral end of an endovascular stent-graft.

In some applications of the present invention, a self-expandableendovascular sealing stent-graft comprises a structural member and afluid flow guide, which is coupled to at least a portion of structuralmember. The structural member has a generally tubular shape, and isshaped so as to define at least two elongated indentations. Each of theelongated indentations extends rostrally to a rostral end of thestructural member, and is tapered in a caudal direction until theindentation converges with the generally tubular shape of the structuralmember. The fluid flow guide covers at least a portion of each of theelongated indentations. The elongated indentations serve to direct bloodflow toward the renal arteries. The structural member typically providesan outwardly-directed radial force against the aorta other than at theelongated indentations, which serves to anchor the stent-graft in theaorta and/or to push the fluid flow guide sealingly against the aorta,thereby preventing current or future type I endoleaks.

In some applications of the present invention, a unilumen endovascularstent-graft comprises rostral and caudal body portions, which compriserostral and caudal structural members, respectively. The stent-graftalso comprises a middle body portion, disposed longitudinally betweenthe rostral and caudal body portions. The stent-graft further comprisesa unilumen fluid flow guide. For some applications, the middle bodyportion comprises a middle structural member, which is integrally joinedto the rostral and caudal structural members. Typically, at least aportion of the middle structural member is configured to be axiallyexpandable. Alternatively, the middle body portion is not structurallysupported. For some applications, when the stent-graft assumes theradially-expanded state, the caudal structural member is flared radiallyoutward at a caudal end thereof.

The unilumen fluid flow guide defines a single, non-bifurcated lumen, soas to define a single fluid flow path through the stent-graft. Thesingle lumen is configured to entirely span the abdominal aorta betweenthe renal arteries and the aorto-iliac bifurcation, and not tosubstantially extend into the aorto-iliac bifurcation, i.e., to extendinto the aorto-iliac bifurcation less than 1 cm, or not at all.

Typically, at least a portion of the middle portion of the fluid flowguide is axially expandable. For example, the portion may be pleated,e.g., accordion-pleated, or may comprise a longitudinally elasticmaterial.

For some applications, when the stent-graft assumes theradially-expanded state, a rostral portion of the fluid flow guide thatat least partially covers the rostral structural member is shaped so asto define rostral radially-diverging and radially-converging portions,which portions together define a rostral bulge that extends radiallyoutward. When the stent-graft assumes the radially-expanded state, acaudal portion of the fluid flow guide that at least partially coversthe caudal structural member is shaped so as to define caudalradially-diverging and radially-converging portions, which portionstogether define a caudal bulge that extends radially outward. Therostral and caudal bulges help to prevent a current or a future type Iendoleak at a rostral end and a caudal end of an aortic aneurysm,respectively.

Typically, the stent-graft is configured such that the bulges expandradially as the rostral end and caudal end of the aneurysm enlarge,respectively, in order to maintain a tight seal with the wall of theaorta, thereby preventing current or future type I endoleaks. At thesame time, the stent-graft is configured to apply a radially-outwardforce that is sufficient to cause the bulges to expand with the aorticwall, but insufficient to itself cause expansion of the aortic wall.

For some applications, a uni-iliac self-expandable extension stent isprovided for use with the unilumen stent-graft. A rostral end of theuni-iliac extension stent is coupled to a caudal end of the caudal bodyportion of the stent-graft along a portion of a circumference of thecaudal end. The uni-iliac extension stent is shaped such that a rostralportion thereof defines a lateral opening therethrough, defined by adiscontinuity of stent cells along a portion of the circumference of theextension stent. After deployment of the stent-graft in the aorta andthe uni-iliac stent in one of the iliac arteries, a bi-iliac stent isadvanced through the iliac artery in which uni-iliac stent ispositioned, passed through the opening, and then into the other iliacartery. The bi-iliac stent and uni-iliac stent help hold the stent-graftanchored in place. For some applications, a portion of the uni-iliacstent-graft caudal to the opening comprises a fluid flow guide, whichmay help treat an iliac aneurysm.

For some applications, the unilumen stent-graft further comprises aplurality of circumferentially-disposed, axially-oriented engagementmembers, coupled to a caudal end of the caudal structural member. Theengagement members are configured to prevent down-migration of thestent-graft through the aorto-iliac bifurcation, which might obstructthe bifurcation.

For some applications, the unilumen stent-graft further comprises aself-expandable uni-iliac extension stent. A rostral end of theuni-iliac extension stent is coupled within the caudal body portion ofthe stent-graft, typically at or near a caudal end of the caudal bulge,such that the rostral end of the uni-iliac extension stent passesthrough the caudal end of the caudal body portion and into an interiorof the caudal body portion. The uni-iliac extension stent may helpanchor the stent-graft in place in the aorta, as well as treat an iliacaneurysm. The stent-graft and the iliac extension stent serve incombination as an aorto-uni-iliac stent-graft.

For some applications, a rostral portion of the uni-iliac extensionstent is shaped so as to provide a lateral opening therethrough, definedby a discontinuity of stent cells along a portion of the circumferenceof the aorto-uni-iliac stent. After deployment of the stent-graft in theaorta and the uni-iliac extension stent in one of the iliac arteries, abi-iliac stent is advanced through the iliac artery in which theuni-iliac stent is positioned, passed through the opening, and then intothe other iliac artery. The bi-iliac stent and the aorto-uni-iliac stenthelp hold the stent-graft anchored in place. For some applications, acaudal portion of the uni-iliac extension stent comprises a fluid flowguide, which may help treat an iliac aneurysm.

For some applications, the unilumen stent-graft further comprises atleast two (e.g., exactly two) iliac engagement members. The iliacengagement members are coupled to a caudal end of the caudal structuralmember, typically on opposites sides of the caudal end. Aself-expandable bi-iliac stent is further provided. The bi-iliac stentis (a) advanced through one of the iliac arteries, (b) passed throughthe iliac engagement members, such that the engagement members and thebi-iliac stent-body engage each other (e.g., interlock with each other),and then (c) into the other iliac artery. The bi-iliac stent helps holdthe stent-graft anchored in place.

There is therefore provided, in accordance with an application of thepresent invention, apparatus for use with a delivery catheter, theapparatus including an endovascular stent-graft, which is configured toinitially be positioned in the delivery catheter in aradially-compressed state, and to assume a radially-expanded state uponbeing deployed from the delivery catheter, and which includes:

a structural member, which includes a plurality of structural stentelements, at least a portion of which structural stent elements define astent body when the stent-graft assumes the radially-expanded state; and

a fluid flow guide, which includes at least one biologically-compatiblesubstantially fluid-impervious flexible sheet, and which is coupled tothe stent body,

wherein, when the stent-graft assumes the radially-expanded state, thefluid flow guide is shaped so as to define radially-diverging andradially-converging portions, which together define a bulge that extendsradially outward, which bulge has a greatest cross-sectional area thatis equal to at least 120% of a cross-sectional area of a narrowestportion of the stent-graft rostral to the bulge.

For some applications, the apparatus further includes the deliverycatheter.

For some applications, a site on the bulge that has the greatestcross-section area is within 5 cm of a rostral end of the fluid flowguide, when the stent-graft assumes the radially-expanded state.

For some applications, the at least a portion of the structural stentelements is a first portion of the structural stent elements, and arostral-most second portion of the structural stent elements define aplurality of anchoring elements that extend radially outwardly when thestent-graft assumes the radially-expanded state. For some applications,the structural member is configured such that the bulge applies aradially-outward force that is less than a radially-outward forceapplied by the anchoring elements, when the stent-graft assumes theradially-expanded state. For example, the radially-outward force appliedby the bulge may be between 25% and 50% of the radially-outward forceapplied by the anchoring elements.

For some applications, a first subset of the structural stent elementsof the stent body are configured to cause the fluid flow guide to definethe bulge, when the stent-graft assumes the radially-expanded state. Forsome applications, (a) a second subset of the structural stent elementsof the stent body are not configured to cause the fluid flow guide todefine the bulge, when the stent-graft assumes the radially-expandedstate, and (b) the structural stent elements of the first subset atleast partially overlap the structural stent elements of the secondsubset lengthwise along the stent body. For some applications, thestructural stent elements include a metal, and the structural stentelements of the first subset contact at least a portion of thestructural stent elements of the second subset, when the stent-graftassumes the radially-compressed state.

For some applications, a spring coefficient of the first subset,measured during application of a radial force at a first point of thefirst subset that is furthest from a central longitudinal axis of thestent-graft, is at least 20% less than a spring coefficient of thesecond subset, measured at a second point of the second subset that isaxially aligned with the first point.

For some applications, the structural stent elements of the secondsubset are shaped so as to define a substantially tubular structure,when the stent-graft assumes the radially-expanded state. For someapplications, the substantially tubular structure is a constant diametercylinder, when the stent-graft assumes the radially-expanded state. Forsome applications, the substantially tubular structure is a flaredcylinder, when the stent-graft assumes the radially-expanded state.

For some applications, when the stent-graft assumes theradially-expanded state, the structural stent elements of the firstsubset are shaped so as to define a plurality of arms that extendradially outward, and are configured to cause the fluid flow guide todefine the bulge. For some applications, the arms extend radiallyoutward in a caudal direction, when the stent-graft assumes theradially-expanded state.

For some applications, the structural stent elements of the secondsubset define an internal structural lumen, and the structural stentelements of the first subset define an external structural lumen, whichis disposed radially outward of the internal structural lumen when thestent-graft assumes the radially-expanded state.

For some applications, the first and second subsets are mutuallyexclusive. Alternatively, the first and second subsets share at leastone of the structural stent elements. For some applications, thestructural stent elements of the first subset are interconnected.Alternatively or additionally, the structural stent elements of thesecond subset are interconnected. For some applications, a third subsetof the structural stent elements of the stent body connect thestructural stent elements of the first subset with the structural stentelements of the second subset. For some applications, the structuralstent elements of the third subset are substantially radially oriented,when the stent-graft assumes the radially-expanded state.

For some applications, the structural stent elements of the first subsetare concentric with the structural stent elements of the second subset,when the stent-graft assumes the radially-expanded state.

For some applications, the structural stent elements of the first subsetradially converge with the structural elements of the second subset atrespective rostral ends of the first and second subsets. Alternativelyor additionally, the structural stent elements of the first subsetradially converge with the structural elements of the second subset atrespective caudal ends of the first and second subsets.

For some applications, when the stent-graft assumes theradially-expanded state, the structural stent elements of the firstsubset are grouped into a plurality of axially-disposed arrays of thestructural stent elements, each of the arrays generally circumscribingat least a 360-degree arc, each of the arrays being substantiallymorphologically deformable independently of the axially adjacent arrays.For some applications, at least a portion of the arrays are structurallyconnected to the axially adjacent arrays. For some applications, atleast a portion of the arrays are not structurally connected to theaxially adjacent arrays.

For some applications, a caudal end of the structural member and acaudal end of the fluid flow guide together define a single lumen, whenthe stent-graft assumes the radially-expanded state. Alternatively, acaudal end of the structural member and a caudal end of the fluid flowguide together define a bifurcated lumen, when the stent-graft assumesthe radially-expanded state.

For some applications, the bulge is adapted to apply an axial forcevector in a rostral direction.

For some applications, the structural member includes a self-expandingmaterial. For some applications, the structural member includes asuper-elastic alloy, such as Nitinol.

There is further provided, in accordance with an application of thepresent invention, apparatus including an endovascular stent-graftsystem, which includes:

an endovascular stent-graft delivery tool, which includes a deliverycatheter; and

an endovascular stent-graft, which is configured to initially bepositioned in the delivery catheter in a radially-compressed state, andto assume a radially-expanded state upon being deployed from thedelivery catheter, and which includes:

-   -   a structural member, which includes a plurality of structural        stent elements, at least a portion of which structural stent        elements define a stent body when the stent-graft assumes the        radially-expanded state; and    -   a fluid flow guide, which includes at least one        biologically-compatible substantially fluid-impervious flexible        sheet, and which is coupled to the stent body,    -   wherein, when the stent-graft assumes the radially-expanded        state, the fluid flow guide is shaped so as to define        radially-diverging and radially-converging portions, which        together define a bulge that extends radially outward, which has        a greatest cross-sectional area that is equal to at least 120%        of a cross-sectional area of a narrowest portion of the        stent-graft rostral to the bulge.

There is still further provided, in accordance with an application ofthe present invention, a method including:

providing an endovascular stent-graft, which is configured to assume aradially-compressed state and a radially-expanded state, and whichincludes (a) a structural member, which includes a plurality ofstructural stent elements, at least a portion of which structural stentelements define a stent body when the stent-graft assumes theradially-expanded state, and (b) a fluid flow guide, which includes atleast one biologically-compatible substantially fluid-imperviousflexible sheet, and which is coupled to the stent body, wherein, whenthe stent-graft assumes the radially-expanded state, the fluid flowguide is shaped so as to define radially-diverging andradially-converging portions, which together define a bulge that extendsradially outward, which has a greatest cross-sectional area that isequal to at least 120% of a cross-sectional area of a narrowest portionof the stent-graft rostral to the bulge;

transvascularly introducing the stent-graft into an aorta of a humansubject, while the stent-graft is positioned in a delivery catheter inthe radially-compressed state; and

deploying the stent-graft from the delivery catheter at least partiallyin the aorta such that the bulge extends radially outward against andsealingly contacts a rostral portion of an abdominal aortic aneurysm inthe aorta when the stent-graft assumes the radially-expanded state.

For some applications, the method further includes identifying thesubject as suffering from the aortic aneurysm, and introducing includestransvascularly introducing the stent-graft responsively to theidentifying.

For some applications, the endovascular stent-graft is one of twoendovascular stent grafts, the structural member is one of twostructural members, and the fluid flow guide is one of two fluid flowguides, the endovascular stent-grafts include the structural members andthe fluid flow guides, respectively, and introducing and deployingincludes introducing and deploying a first one of the stent-grafts, andfurther including:

transvascularly introducing a second one of the stent-grafts, while thesecond stent-graft is in the radially-compressed state, into the aorta,adjacent to an aorto-iliac bifurcation, such that the second stent-graftis oriented in an axial direction opposite to that of the first stentgraft; and

deploying the second stent-graft at least partially in the aorta suchthat the bulge of the second stent-graft extends radially outwardagainst a caudal portion of the abdominal aortic aneurysm in the aortawhen the second stent-graft assumes the radially-expanded state, andsuch that an end of one of the stent-grafts is deployed within an end ofthe other of the stent-grafts, in order to provide fluid-tight couplingof the stent-grafts with each other when the stent-grafts assume theradially-expanded state.

For some applications, the structural member of the second stent-graftis shaped so as to define a plurality of anchoring elements, anddeploying the second stent-graft includes positioning the anchoringelements to engage an aorta-iliac bifurcation.

For some applications, a first subset of the structural stent elementsof the stent body are configured to cause the fluid flow guide to definethe bulge, when the stent-graft assumes the radially-expanded state.

There is additionally provided, in accordance with an application of thepresent invention, apparatus for use with a delivery catheter, theapparatus including an endovascular stent-graft, which is configured toinitially be positioned in the delivery catheter in aradially-compressed state, and to assume a radially-expanded state uponbeing deployed from the delivery catheter, and which includes:

a structural member, which includes a plurality of structural stentelements, a rostral-most first portion of which members define aplurality of anchoring elements that extend radially outwardly androstrally when the stent-graft assumes the radially-expanded state, anda second portion of which members define a tubular body when thestent-graft assumes the radially-expanded state;

a fluid flow guide, which includes at least one biologically-compatiblesubstantially fluid-impervious flexible sheet, and which is coupled tothe tubular body; and

at least one skirt, which includes at least one biologically-compatiblesubstantially fluid-impervious flexible sheet, and which extends fromthe structural member at a circumferential juncture between theanchoring elements and the tubular body, and which terminates in aperipheral edge that has a greater circumference than that of thecircumferential juncture when the stent-graft assumes theradially-expanded state,

wherein the skirt extends rostrally from the juncture when thestent-graft is initially positioned in the delivery catheter in theradially-compressed state, and

wherein, upon application of a caudally-directed force to the peripheraledge of the skirt after deployment of the stent-graft from the deliverycatheter, the skirt extends caudally from the juncture.

For some applications, the apparatus further includes the deliverycatheter.

For some applications, the circumference of the peripheral edge of theskirt is greater than a circumference of all other elements of thestent-graft, when the stent-graft assumes the radially-expanded state.

For some applications, the skirt is sealingly coupled to a rostral endof the fluid flow guide around the entire circumferential juncture.

For some applications, the skirt further includes a scaffold, which atleast partially supports the flexible sheet. For some applications, thescaffold extends from at least a portion of the juncture to at least aportion of the peripheral edge of the skirt. For some applications, thejuncture includes a pivot, to which the scaffold is rotatably coupled soas to allow the skirt to transition from extending rostrally toextending caudally. For some applications, the scaffold includes aself-expanding material. For some applications, the scaffold includes asuper-elastic alloy, such as Nitinol.

There is yet additionally provided, in accordance with an application ofthe present invention, apparatus including an endovascular stent-graftsystem, which includes:

an endovascular stent-graft delivery tool, which includes a deliverycatheter; and

an endovascular stent-graft, which is configured to initially bepositioned in the delivery catheter in a radially-compressed state, andto assume a radially-expanded state upon being deployed from thedelivery catheter, and which includes:

-   -   a structural member, which includes a plurality of structural        stent elements, a rostral-most first portion of which members        define a plurality of anchoring elements that extend radially        outwardly and rostrally when the stent-graft assumes the        radially-expanded state, and a second portion of which members        define a tubular body when the stent-graft assumes the        radially-expanded state;    -   a fluid flow guide, which includes at least one        biologically-compatible substantially fluid-impervious flexible        sheet, and which is coupled to the tubular body; and    -   at least one skirt, which includes at least one        biologically-compatible substantially fluid-impervious flexible        sheet, and which extends from the structural member at a        circumferential juncture between the anchoring elements and the        tubular body, and which terminates in a peripheral edge that has        a greater circumference than that of the circumferential        juncture when the stent-graft assumes the radially-expanded        state,    -   wherein the skirt extends rostrally from the juncture when the        stent-graft is initially positioned in the delivery catheter in        the radially-compressed state, and    -   wherein, upon application of a caudally-directed force to the        peripheral edge of the skirt after deployment of the stent-graft        from the delivery catheter, the skirt extends caudally from the        juncture.

There is also provided, in accordance with an application of the presentinvention, a method including:

providing an endovascular stent-graft, which is configured to assume aradially-compressed state and a radially-expanded state, and whichincludes (a) a structural member, which includes a plurality ofstructural stent elements, a first rostral-most portion of which membersdefine a plurality of anchoring elements, and a second portion of whichmembers define a tubular body when the stent-graft assumes theradially-expanded state, (b) a fluid flow guide, which includes at leastone biologically-compatible substantially fluid-impervious flexiblesheet, and which is coupled to the tubular body, and (c) at least oneskirt, which includes at least one biologically-compatible substantiallyfluid-impervious flexible sheet, and which extends from the structuralmember at a circumferential juncture between the anchoring elements andthe tubular body, and which terminates in a peripheral edge that has agreater circumference than that of the circumferential juncture when thestent-graft assumes the radially-expanded state;

transvascularly introducing the stent-graft into an aorta of a humansubject, while the stent-graft is positioned in a delivery catheter inthe radially-compressed state such that the skirt extends rostrally fromthe juncture;

at least partially deploying the stent-graft from the delivery catheterin the aorta such that the skirt at least partially radially expands,thereby bringing the peripheral edge of the skirt into contact with awall of the aorta caudal to renal arteries of the subject, and such thatthe anchoring elements extend radially outwardly and rostrally; and

inverting the skirt such that the skirt extends caudally from thejuncture, by applying a caudally-directed force to the peripheral edgeof the skirt after at least partially deploying the stent-graft from thedelivery catheter, in order to facilitate sealing of blood leakagearound the stent-graft when it assumes the radially-expanded state.

For some applications, the method further includes identifying thesubject as suffering from an aortic aneurysm, and introducing includestransvascularly introducing the stent-graft responsively to theidentifying.

For some applications, applying the caudally-directed force includesadvancing the stent-graft rostrally such that a wall of the aortaapplies the caudally-directed force to the peripheral edge of the skirt.

For some applications, the skirt further includes a scaffold, which atleast partially supports the flexible sheet, and the juncture includes apivot, to which the scaffold is rotatably coupled, and inverting theskirt includes rotating the skirt around on the pivot to transition theskirt from extending rostrally to extending caudally.

There is further provided, in accordance with an application of thepresent invention, apparatus for use with a delivery catheter and aprimary stent-graft, the apparatus including a doubly-flaredendovascular stent-graft, which is configured to initially be positionedin the delivery catheter in a radially-compressed state, and to assume aradially-expanded state upon being deployed from the delivery catheter,and which includes:

a structural member, which includes a plurality of structural stentelements, and which, when the doubly-flared endovascular stent-graftassumes the radially-expanded state, is shaped so as to define (a) aflared rostral portion, which flares radially outward in a rostraldirection, and (b) a flared caudal portion, which flares radiallyoutward in a caudal direction;

at least one biologically-compatible substantially fluid-imperviousflexible sheet, which is coupled to at least the flared caudal portion;and

a stent-engagement member, which is generally tubular when thedoubly-flared endovascular stent-graft assumes the radially-expandedstate, which is disposed at least partially within the flared caudalportion, and which is configured to be sealingly coupled to the primarystent-graft.

For some applications, the apparatus further includes the primarystent-graft.

For some applications, the apparatus further includes the deliverycatheter.

For some applications, the structural member, when the doubly-flaredendovascular stent-graft assumes the radially-expanded state, is shapedso as to further define a body portion, disposed longitudinally betweenthe flared rostral and caudal portions, and having a diameter thatvaries by less than 15% along an entire length of the body portion.

For some applications, a spring coefficient of the flared caudalportion, measured during application of a radial force at a first pointon the flared caudal portion that is furthest from a centrallongitudinal axis of the doubly-flared endovascular stent-graft, is atleast 20% less than at least one spring coefficient selected from thegroup consisting of: (a) a spring coefficient of the body portion,measured during application of the radial force at a second point on thebody portion that is furthest from the axis, and (b) a springcoefficient of the flared rostral portion, measured during applicationof the radial force at a third point on the flared rostral portion thatis furthest from the axis.

For some applications, the flared rostral portion defines a plurality ofanchoring elements that extend radially outwardly, when thedoubly-flared endovascular stent-graft assumes the radially-expandedstate.

For some applications, the at least one flexible sheet of the fluid flowguide is a first at least flexible sheet, and the doubly-flaredendovascular stent-graft further includes at least a secondbiologically-compatible substantially fluid-impervious flexible sheet,which at least partially covers the stent-engagement member.

For some applications, the stent engagement member includes a scaffold.For some applications, the scaffold includes a self-expanding material.For some applications, the scaffold includes a super-elastic alloy, suchas Nitinol.

For some applications, an axial length of the flared caudal portionvaries around a circumference of the flared caudal portion.

For some applications, the caudal end of the structural member isinternally curved.

For some applications, the flared caudal portion is externally convex.

For some applications, the flared caudal portion includes a rostralsub-portion that is externally concave and a more caudal sub-portionthat is externally convex.

For some applications, the structural member includes a self-expandingmaterial. For some applications, the structural member includes asuper-elastic alloy, such as Nitinol. For some applications, thestructural member is woven. For some applications, the structural memberis braided.

There is still further provided, in accordance with an application ofthe present invention, a method including:

providing a doubly-flared endovascular stent-graft, which is configuredto assume a radially-compressed state and a radially-expanded state, andwhich includes (i) a structural member, which includes a plurality ofstructural stent elements, and which, when the doubly-flaredendovascular stent-graft assumes the radially-expanded state, is shapedso as to define (a) a flared rostral portion, which flares radiallyoutward in a rostral direction, and (b) a flared caudal portion, whichflares radially outward in a caudal direction, and (ii) a fluid flowguide, which includes at least one biologically-compatible substantiallyfluid-impervious flexible sheet, and which is coupled to at least theflared caudal portion;

transvascularly introducing the doubly-flared endovascular stent-graftinto an aorta of a human subject, while the doubly-flared endovascularstent-graft is positioned in a delivery catheter in theradially-compressed state; and

transitioning the doubly-flared endovascular stent-graft to theradially-expanded state by deploying the doubly-flared endovascularstent-graft from the delivery catheter in the aorta, such that theflared caudal portion is positioned caudal to both of anastomoses ofrenal arteries, and the flared rostral portion is positioned rostral toboth of the anastomoses of the renal arteries.

For some applications, the method further includes identifying thesubject as suffering from an aortic aneurysm, and introducing includestransvascularly introducing the doubly-flared endovascular stent-graftresponsively to the identifying.

For some applications, the structural member, when the doubly-flaredendovascular stent-graft assumes the radially-expanded state, is shapedso as to further define a body portion, disposed longitudinally betweenthe flared rostral and caudal portions, and having a diameter thatvaries by less than 15% along an entire length thereof, and deployingincludes deploying the doubly-flared endovascular stent-graft such thatthe body portion spans both the anastomoses of the renal arteries.

For some applications, providing the doubly-flared endovascularstent-graft includes providing the doubly-flared endovascularstent-graft having a diameter of the body portion that is at least 15%less than a diameter of the aorta between the renal arteries, and havinga diameter of a caudal end of the structural member that is at least 20%larger than a diameter of the aorta immediately caudal to a more caudalone of the renal arteries.

For some applications, the doubly-flared endovascular further includes astent-engagement member, which is generally tubular when thedoubly-flared endovascular stent-graft assumes the radially-expandedstate, and which is disposed at least partially within the flared caudalportion, and further including transvascularly delivering a primarystent-graft to the aorta, and sealingly coupling the primary stent-graftto the stent-engagement member.

For some applications, the method further includes:

providing an additional endovascular stent-graft that has a single-lumenrostral end and a bifurcated caudal end;

transvascularly introducing the single-lumen rostral end of theadditional stent-graft into the aorta, and sealingly coupling therostral end to a lumen defined by the fluid flow guide;

deploying the bifurcated caudal end of the additional stent-graft intoboth iliac arteries.

There is additionally provided, in accordance with an application of thepresent invention, apparatus including a self-expanding lumen-engagementprosthesis member, which is adjustable between a radially-expanded stateand a radially-compressed state, which is generally tubular, and whichincludes:

a plurality of support members, which, when the prosthesis memberassumes the radially-expanded state, are distributed around acircumference of the prosthesis member, and are shaped so as to definerespective curves having concavities that face radially outward;

a plurality of rostral barbs, which extend caudally and radiallyoutwardly from respective ones of the support members when theprosthesis member assumes the radially-expanded state; and

a plurality of caudal barbs, which extend rostrally and radially outwardfrom respective ones of the support members when the prosthesis memberassumes the radially-expanded state, and which are disposed morecaudally than the rostral barbs.

For some applications, the rostral barbs are disposed at respectiverostral ends of the support members.

For some applications, the caudal barbs are disposed at respectivecaudal ends of the support members.

For some applications, the rostral barbs extend caudally at an angle ofbetween 50 and 70 degrees with respect to a central longitudinal axis ofthe prosthesis member.

For some applications, the caudal barbs extend rostrally at an angle ofbetween 50 and 70 degrees with respect to a central longitudinal axis ofthe prosthesis member.

For some applications, the apparatus further includes a stent-graft, arostral end of which is coupled to a caudal end of the prosthesismember. For some applications, the stent-graft includes a fluid flowguide, which includes at least one biologically-compatible substantiallyfluid-impervious flexible sheet.

For some applications, the prosthesis member includes a self-expandingmaterial. For some applications, the prosthesis member includes asuper-elastic alloy, such as Nitinol. For some applications, theprosthesis member includes a braided material. For some applications,the prosthesis member includes a woven material.

For some applications, the prosthesis member is configured tolongitudinally shorten as the prosthesis member transitions from theradially-compressed state to the radially-expanded state, therebybringing the rostral and caudal ends of the structural member closer toeach other.

For some applications, the apparatus further includes an endovascularstent-graft system, configured to endoluminally treat an aorticaneurysm, the system including the lumen-engagement prosthesis member.

There is yet additionally provided, in accordance with an application ofthe present invention, a method including:

providing a lumen-engagement prosthesis member, which is adjustablebetween a radially-expanded state and a radially-compressed state, andwhich includes (a) a structural member, which has rostral and caudalends and a central longitudinal axis, and which is generally tubular andexternally concave when the prosthesis member assumes theradially-expanded state, (b) a plurality of rostral barbs, which extendcaudally and radially outwardly from the central longitudinal axis whenthe prosthesis member assumes the radially-expanded state, and (c) aplurality of caudal barbs, which extend rostrally and radially outwardfrom the central longitudinal axis when the prosthesis member assumesthe radially-expanded state;

transvascularly introducing the prosthesis member into an aorta of ahuman subject, while the prosthesis member is positioned in a deliverycatheter in the radially-compressed state; and

transitioning the prosthesis member to the radially-expanded state bydeploying the prosthesis member from the delivery catheter in the aortawithin 2 cm of renal arteries of the subject, such that the prosthesismember engages a wall of the aorta.

For some applications, the method further includes identifying thesubject as suffering from an aortic aneurysm, and introducing includestransvascularly introducing the prosthesis member responsively to theidentifying.

For some applications, deploying includes deploying the prosthesismember such that the prosthesis member engages the aortic wall rostralto the renal arteries.

For some applications, deploying includes deploying the prosthesismember such that the prosthesis member engages the aortic wall caudal tothe renal arteries.

For some applications, providing the prosthesis member includesproviding the prosthesis member sized such that a diameter of thestructural member when the prosthesis member assumes theradially-expanded state is greater than a diameter of the aorta at sitesat which the prosthetic member engages the aortic wall.

For some applications, transitioning the prosthesis includes causing theprosthesis member to longitudinally shorten as the prosthesis membertransitions from the radially-compressed state to the radially-expandedstate, thereby bringing the rostral and caudal ends of the structuralmember closer to each other.

There is also provided, in accordance with an application of the presentinvention, apparatus for use with a delivery catheter, the apparatusincluding an endovascular sealing stent-graft, which is configured toinitially be positioned in the delivery catheter in aradially-compressed state, and to assume a radially-expanded state uponbeing deployed from the delivery catheter, and which includes:

a structural member, which includes a plurality of structural stentelements, and which, when the stent-graft assumes the radially-expandedstate, has a generally tubular shape, and is shaped so as to define atleast two elongated indentations, each of which extends rostrally to arostral end of the structural member, and is tapered in a caudaldirection until the indentation converges with the generally tubularshape of the structural member, and each of which has an axial length ofat least 2 cm; and

a fluid flow guide, which includes at least one biologically-compatiblesubstantially fluid-impervious flexible sheet, and which is coupled toat least a portion of the structural member, and covers at least aportion of each of the elongated indentations.

For some applications, the apparatus further includes the deliverycatheter.

For some applications, a rostral end of the fluid flow guide is disposedwithin 4 cm of the rostral end of the structural member.

For some applications, a caudal end of the fluid flow guide is disposedwithin 2 cm of a caudal end of the structural member.

For some applications, the stent-graft further includes a plurality ofanchoring elements, which are generally radially oriented when thestent-graft assumes the radially-expanded state.

For some applications, a rostral end of each of the elongatedindentations spans an arc of between 10 and 40 degrees.

For some applications, centers of two of the elongated indentations areoffset by an angle of between 70 and 220 degrees, as measured withrespect to a central longitudinal axis of the structural member. Forsome applications, the angle is between 150 and 170 degrees.

For some applications, a diameter of the structural member is between2.5 and 3 cm, when the stent-graft assumes the radially-expanded state.

For some applications, an axial length of the structural member isbetween 4 and 7 cm, when the stent-graft assumes the radially-expandedstate.

For some applications, the axial length of each of the elongatedindentations no more than 4 cm, when the stent-graft assumes theradially-expanded state.

For some applications, a rostral end of each of the elongatedindentations is indented between 0.5 and 1 cm from the generally tubularshape of the structural member, when the stent-graft assumes theradially-expanded state.

For some applications, the structural member includes a self-expandingmaterial. For some applications, the structural member includes asuper-elastic alloy, such as Nitinol.

There further provided, in accordance with an application of the presentinvention, a method including:

providing an endovascular sealing stent-graft, which is configured toassume a radially-compressed state and a radially-expanded state, andwhich includes (a) a structural member, which includes a plurality ofstructural stent elements, and which, when the stent-graft assumes theradially-expanded state, has a generally tubular shape, and is shaped soas to define at least two elongated indentations, each of which extendsrostrally to a rostral end of the structural member, and is tapered in acaudal direction until the indentation converges with the generallytubular shape of the structural member, and each of which has an axiallength of at least 2 cm, and (b) a fluid flow guide, which includes atleast one biologically-compatible substantially fluid-imperviousflexible sheet, and which is coupled to at least a portion of thestructural member, and covers at least a portion of the elongatedindentations;

transvascularly introducing the stent-graft into an aorta of a humansubject, in a vicinity of renal arteries of the subject, while thestent-graft is positioned in a delivery catheter in theradially-compressed state;

transitioning the stent-graft to the radially-expanded state bydeploying the stent-graft from the delivery catheter in the aorta, suchthat two of the elongated indentations are radially aligned with therenal arteries, with rostral ends of the elongated indentations rostralto the renal arteries, respectively, and caudal ends of the elongatedindentations caudal to the renal arteries, respectively.

For some applications, the method further includes identifying thesubject as suffering from an aortic aneurysm, and introducing includestransvascularly introducing the stent-graft responsively to theidentifying.

For some applications, the stent-graft is one of a plurality ofstent-grafts having different, respective angles of offset between twoof the elongated indentations, and providing the stent-graft includes:assessing an angle between the renal arteries; and selecting one of thestent-grafts having an angle of offset closest to the assessed anglebetween the renal arteries.

There is still further provided, in accordance with an application ofthe present invention, apparatus for use with a delivery catheter, theapparatus including an endovascular prosthesis, which is configured toinitially be positioned in the delivery catheter in aradially-compressed state, and to assume a radially-expanded state uponbeing deployed from the delivery catheter, and which includes:

a structural member, which includes a plurality of structural stentelements, at least a portion of which structural stent elements define astent body when the prosthesis assumes the radially-expanded state;

a plurality of blunt tissue engagement members, which are disposedexternally to the stent body when the prosthesis assumes theradially-expanded state; and

a plurality of communicating members, which respectively connect thetissue engagement members to the stent body, the communicating membersbeing generally radially-oriented when the prosthesis assumes theradially-expanded state.

For some applications, the apparatus further includes the deliverycatheter.

For some applications, the endovascular prosthesis further includes afluid flow guide, which includes at least one biologically-compatiblesubstantially fluid-impervious flexible sheet, and which is coupled tothe stent body.

For some applications, each of at least a portion of the tissueengagement members has surface area of at least 0.5 mm2.

For some applications, each of at least a portion of the tissueengagement members extends in one or more directions generally parallelto a surface of the stent body.

For some applications, respective distances between a surface of thestent body and all locations of each of at least a portion of the tissueengagement member vary by less than 30%.

For some applications, the tissue engagement members are arranged as acircumferential array around the stent body.

For some applications, the tissue engagement members are arranged as anaxial array along the stent body.

For some applications, the apparatus further includes a plurality ofconnecting elements, which couple at least a portion of the tissueengagement members to respective adjacent ones of the tissue engagementmembers.

For some applications, when the prosthesis assumes the radially-expandedstate, a spring coefficient of each of the communicating members,measuring during application of a radial force, is at least 20% lessthan a spring coefficient of the stent body, measured during applicationof the radial force at a point on the stent body at which thecommunicating member is connected.

For some applications, the tissue engagement members radially protrude adistance of between 1 and 4 mm from the stent body, when the prosthesisassumes the radially-expanded state.

For some applications, the at least a portion of the structural stentelements is a first portion of the structural stent elements, and arostral-most second portion of the structural stent elements define aplurality of anchoring elements that extend radially outwardly when theprosthesis assumes the radially-expanded state.

For some applications, the tissue engagement members are arcuate, andextend laterally around the stent body. For some applications, thetissue engagement members are generally linear, and extend axially alongthe stent body. For some applications, the tissue engagement members arepolygonal.

For some applications, the structural member includes a self-expandingmaterial. For some applications, the structural member includes asuper-elastic alloy, such as Nitinol.

There is additionally provided, in accordance with an application of thepresent invention, apparatus including an endovascular prostheticsystem, which includes:

an endovascular prosthesis delivery tool, which includes a deliverycatheter; and

an endovascular prosthesis, which is configured to initially bepositioned in the delivery catheter in a radially-compressed state, andto assume a radially-expanded state upon being deployed from thedelivery catheter, and which includes:

-   -   a structural member, which includes a plurality of structural        stent elements, at least a portion of which structural stent        elements define a stent body when the prosthesis assumes the        radially-expanded state;    -   a plurality of non-barbed tissue engagement members, which are        disposed externally to the stent body when the prosthesis        assumes the radially-expanded state; and    -   a plurality of communicating members, which respectively connect        the tissue engagement members to the stent body, the        communicating members being generally radially-oriented when the        prosthesis assumes the radially-expanded state.

There is yet additionally provided, in accordance with an application ofthe present invention, a method including:

providing an endovascular prosthesis, which is configured to assume aradially-compressed state and a radially-expanded state, and whichincludes (a) a structural member, which includes a plurality ofstructural stent elements, at least a portion of which structural stentelements define a stent body when the prosthesis assumes theradially-expanded state, (b) a plurality of non-barbed tissue engagementmembers, which are disposed externally to the stent body when theprosthesis assumes the radially-expanded state, and (c) a plurality ofcommunicating members, which respectively connect the tissue engagementmembers to the stent body, the communicating members being generallyradially-oriented when the prosthesis assumes the radially-expandedstate;

transvascularly introducing the prosthesis into an aorta of a humansubject, while the prosthesis is positioned in a delivery catheter inthe radially-compressed state; and

at least partially deploying the prosthesis from the delivery catheterin the aorta such that the tissue engagement members enter a wall of theaorta.

For some applications, the method further includes identifying thesubject as suffering from an aortic aneurysm, and introducing includestransvascularly introducing the prosthesis responsively to theidentifying.

For some applications, deploying includes at least partially deployingthe prosthesis such that the tissue engagement members do not passentirely through the aortic wall.

For some applications, providing the prosthesis including providing theprosthesis in which each of at least a portion of the tissue engagementmembers extends in one or more directions generally parallel to asurface of the stent body.

For some applications, providing the prosthesis including providing theprosthesis in which the tissue engagement members are arranged as acircumferential array around the stent body.

For some applications, providing the prosthesis including providing theprosthesis in which the tissue engagement members are arranged as anaxial array along the stent body.

For some applications, providing the prosthesis including providing theprosthesis in which the tissue engagement members are arcuate, andextend laterally around the stent body.

For some applications, providing the prosthesis including providing theprosthesis in which the tissue engagement members are generally linear,and extend axially along the stent body.

For some applications, providing the prosthesis including providing theprosthesis in which the tissue engagement members are polygonal.

There is yet additionally provided, in accordance with an application ofthe present invention, apparatus for use with a delivery catheter, theapparatus including an endovascular stent-graft, which is configured toinitially be positioned in the delivery catheter in aradially-compressed state, and to assume a radially-expanded state uponbeing deployed from the delivery catheter, and which includes:

rostral and caudal body portions, which include rostral and caudalstructural members, respectively, each of which includes a plurality ofstructural stent elements;

a middle body portion, disposed longitudinally between the rostral andcaudal body portions; and

a unilumen fluid flow guide, which includes at least onebiologically-compatible substantially fluid-impervious flexible sheetshaped so as to define a single, non-bifurcated lumen, and which iscoupled to the rostral and caudal structural members, at least partiallycovers the rostral structural member, at least partially covers thecaudal structural member, and includes a middle portion that extendslongitudinally along an entire length of the middle body portion,

wherein, when the stent-graft assumes the radially-expanded state, arostral portion of the fluid flow guide that at least partially coversthe rostral structural member is shaped so as to define rostralradially-diverging and radially-converging portions, which portionstogether define a rostral bulge that extends radially outward, whichbulge has a greatest cross-sectional area that is equal to at least 120%of a cross-sectional area of a narrowest portion of the rostral bodyportion rostral to the bulge, and

wherein, when the stent-graft assumes the radially-expanded state, acaudal portion of the fluid flow guide that at least partially coversthe caudal structural member is shaped so as to define caudalradially-diverging and radially-converging portions, which portionstogether define a caudal bulge that extends radially outward, whichbulge has a greatest cross-sectional area that is equal to at least 120%of a cross-sectional area of a narrowest portion of the caudal bodyportion caudal to the bulge.

For some applications, the rostral structural member is shaped so as todefine a generally cylindrical subportion rostral to the rostral bulge,when the stent-graft assumes the radially-expanded state. For someapplications, the rostral structural member is shaped so as to define agenerally cylindrical subportion caudal to the rostral bulge, when thestent-graft assumes the radially-expanded state.

For some applications, a spring coefficient of the rostral bulge,measured during application of a radial force at a first point of therostral bulge that is furthest from a central longitudinal axis of thestent-graft, is at least 20% less than a spring coefficient of thegenerally cylindrical subportion, measuring during application of theradial force at a second point of the generally cylindrical subportionthat is furthest from the axis.

For some applications, the caudal structural member is shaped so as todefine a generally cylindrical subportion caudal to the caudal bulge,when the stent-graft assumes the radially-expanded state.

For some applications, the caudal structural member is shaped so as todefine a generally cylindrical subportion rostral to the caudal bulge,when the stent-graft assumes the radially-expanded state.

For some applications, a spring coefficient of the caudal bulge,measured during application of a radial force at a first point of thecaudal bulge that is furthest from a central longitudinal axis of thestent-graft, is at least 20% less than a spring coefficient of thegenerally cylindrical subportion, measuring during application of theradial force at a second point of the generally cylindrical subportionthat is furthest from the axis.

For some applications, the middle body portion includes a middlestructural member, which includes a plurality of structural stentelements, and which is integrally joined to the rostral and caudalstructural members.

For some applications, at least a portion of the middle structuralmember is configured to be axially expandable.

For some applications, the fluid flow guide is sparsely attached to themiddle structural member.

For some applications, the middle body portion is not structurallysupported by any structural stent elements.

For some applications, at least a portion of the middle portion of thefluid flow guide is axially expandable. For some applications, at leasta portion of the middle portion of the fluid flow guide iskink-resistant.

For some applications, the middle portion of the fluid flow guide isgenerally cylindrical, when the stent-graft assumes theradially-expanded state.

For some applications, the apparatus further includes the deliverycatheter.

For some applications, the caudal structural member is flared radiallyoutward at a caudal end thereof, when the stent-graft assumes theradially-expanded state. For some applications, the caudal body portionfurther includes a first set of circumferentially-disposed barbs thatextend radially outwardly and caudally when the stent-graft assumes theradially-expanded state, and the caudal end of the caudal structuralmember includes a second set of barbs that extend radially outward androstrally when the stent-graft assumes the radially-expanded state. Forsome applications, a caudal end of the caudal structural member has ashape selected from the group consisting of: a non-circular ellipse, anda peanut shell shape.

For some applications, stent-graft further includes a plurality ofanchoring elements that extend radially outwardly when the stent-graftassumes the radially-expanded state, the anchoring elements disposedrostral to the rostral body portion. For some applications, the rostralbody portion is configured such that the rostral bulge applies aradially-outward force that is less than a radially-outward forceapplied by the anchoring elements, when the stent-graft assumes theradially-expanded state. For some applications, the rostral body portionfurther includes a first set of circumferentially-disposed barbs thatextend radially outwardly and rostrally when the stent-graft assumes theradially-expanded state, and the anchoring elements include a second setof barbs that extend radially outwardly and caudally when thestent-graft assumes the radially-expanded state.

For some applications, a portion of the rostral structural stentelements are configured to cause the fluid flow guide to define therostral bulge, when the stent-graft assumes the radially-expanded state,and a portion of the caudal structural stent elements are configured tocause the fluid flow guide to define the caudal bulge, when thestent-graft assumes the radially-expanded state.

For some applications, the apparatus further includes an expandableuni-iliac extension stent, a rostral end of which is coupled to a caudalend of the caudal body portion along a portion of a circumference of thecaudal end. For some applications, the portion of the circumference isless than 40 degrees of the circumference. For some applications, theapparatus further includes at least one radiopaque marker, disposed onat least one stent selected from the group consisting of: theendovascular stent-graft, and the uni-iliac extension stent, and adaptedto aid in achieving a desired rotational orientation of the stent-graftand the uni-iliac extension stent. For some applications, the apparatusfurther includes the delivery catheter. For some applications, thedelivery catheter includes at least one radiopaque marker, adapted toaid in achieving a desired rotational orientation of the stent-graft andthe uni-iliac extension stent. For some applications, the apparatusfurther includes an expandable bi-iliac extension stent, which isconfigured to be passed through a rostral portion of the uni-iliacextension stent. For some applications, the bi-iliac stent includes asuper-elastic alloy, such as Nitinol. For some applications, thebi-iliac extension stent includes an extension fluid flow guide, whichincludes at least one biologically-compatible substantiallyfluid-impervious flexible sheet, and covers at least a portion of thebi-iliac extension stent. For some applications, the uni-iliac extensionstent includes an extension fluid flow guide, which includes at leastone biologically-compatible substantially fluid-impervious flexiblesheet, and covers at least a portion of the uni-iliac extension stent.For some applications, the uni-iliac extension stent includes asuper-elastic alloy, such as Nitinol.

For some applications, the structural members include a super-elasticalloy, such as Nitinol.

For some applications, the apparatus further includes a plurality ofcircumferentially-disposed, axially-oriented engagement members, coupledto a caudal end of the caudal structural member. For some applications,the apparatus further includes a self-expandable bi-iliac stent, whichincludes a bi-iliac stent body, and (a) at least a portion of thecircumferentially-disposed, axially-oriented engagement members and (b)the bi-iliac stent body are configured to engage each other. For someapplications, the bi-iliac stent further includes a fluid flow guide,which includes at least one biologically-compatible substantiallyfluid-impervious flexible sheet, and which is coupled to the bi-iliacstent body.

For some applications, the apparatus further includes an uni-iliacextension stent, a rostral end of which is coupled within the caudalbody portion, such that the rostral end passes through a caudal end ofthe caudal body portion. For some applications, the uni-iliac extensionstent includes a plurality of stent cells, and a rostral portion of theextension stent is shaped so as to provide a lateral openingtherethrough, defined by a discontinuity of the stent cells along aportion of a circumference of the extension stent. For someapplications, the portion of the circumference includes more than 320degrees of the circumference.

For some applications, the stent-graft further includes at least twoiliac engagement members, which are coupled to a caudal end of thecaudal structural member, and the apparatus further includes aself-expandable bi-iliac stent, which is sized and shaped to beendovascularly introduced and subsequently deployed through iliacengagement members, so as to be coupled to the endovascular stent-graft.

There is also provided, in accordance with an application of the presentinvention, apparatus for use with a delivery catheter, the apparatusincluding an endovascular stent-graft, which is configured to initiallybe positioned in the delivery catheter in a radially-compressed state,and to assume a radially-expanded state upon being deployed from thedelivery catheter, and which includes:

rostral and caudal body portions, which include rostral and caudalstructural members, respectively, each of which includes a plurality ofstructural stent elements;

a middle body portion, disposed longitudinally between the rostral andcaudal body portions; and

a unilumen fluid flow guide, which includes at least onebiologically-compatible substantially fluid-impervious flexible sheetshaped so as to define a single, non-bifurcated lumen, and which iscoupled to the rostral and caudal structural members, at least partiallycovers the rostral structural member, at least partially covers thecaudal structural member, and includes a middle portion that extendslongitudinally along an entire length of the middle body portion,

wherein at least a portion of the middle portion of the fluid flow guideis axially expandable.

For some applications, the stent-graft is configured such that an axiallength of the stent-graft between a rostral end of the rostral bodyportion and a caudal end of the caudal body portion is variable betweena minimum length and a maximum length, the minimum length between 2 and5 cm, and the maximum length between 10 and 20 cm.

For some applications, the stent-graft is configured such that an axiallength of the axially-expandable portion of the middle portion isvariable up to a maximum length change, which maximum length change isbetween 2 and 20 cm.

For some applications, the stent-graft is configured such that the flowguide, at the rostral body portion, forms a seal with a wall of theaorta caudal to the renal arteries, and, at the caudal body portion,forms a seal with the aortic wall rostral to the iliac arteries.

For some applications, the middle body portion includes a middlestructural member, which includes a plurality of structural stentelements, and which is integrally joined to the rostral and caudalstructural members.

For some applications, the middle structural member is configured to beaxially expandable.

For some applications, the middle body portion does not include anystructural stent elements.

For some applications, the apparatus further includes the deliverycatheter.

For some applications, stent-graft further includes a plurality ofanchoring elements that extend radially outwardly when the stent-graftassumes the radially-expanded state, the anchoring elements disposedrostral to the rostral body portion.

For some applications, the stent-graft further includes a plurality ofanchoring elements that extend radially outwardly when the stent-graftassumes the radially-expanded state, the anchoring elements disposedcaudal to the caudal body portion.

There is further provided, in accordance with an application of thepresent invention, a method including:

providing an endovascular stent-graft, which is configured to assume aradially-compressed state and a radially-expanded state, and whichincludes (a) rostral and caudal body portions, which include rostral andcaudal structural members, respectively, each of which includes aplurality of structural stent elements, (b) a middle body portion,disposed longitudinally between the rostral and caudal body portions,and (c) a unilumen fluid flow guide, which includes at least onebiologically-compatible substantially fluid-impervious flexible sheetshaped so as to define a single, non-bifurcated lumen, and which iscoupled to the rostral and caudal structural members, at least partiallycovers the rostral structural member, at least partially covers thecaudal structural member, and includes a middle portion that extendslongitudinally along an entire length of the middle body portion,wherein at least a portion of the middle portion of the fluid flow guideis axially expandable;

transvascularly introducing the stent-graft into an aorta of a humansubject, while the stent-graft is positioned in a delivery catheter inthe radially-compressed state;

deploying the rostral body portion from the delivery catheter into theaorta in a vicinity of renal arteries of the subject;

deploying the middle body portion from the delivery catheter into theaorta caudal to the renal arteries; and

deploying the caudal body portion from the delivery catheter into theaorta in a vicinity of iliac arteries of the subject, such that theaxially-expandable portion of the middle portion of the fluid flow guideexpands so that the single, non-bifurcated lumen entirely spans anabdominal aorta between the renal arteries and an aorto-iliacbifurcation, without extending into the aorto-iliac bifurcation morethan 1 cm.

For some applications, the method further includes identifying thesubject as suffering from an aortic aneurysm, and introducing includestransvascularly introducing the stent-graft responsively to theidentifying.

For some applications,

providing includes providing the stent-graft in which a rostral portionof the fluid flow guide that at least partially covers the rostralstructural member is shaped so as to define a rostral bulge that extendsradially outward, and a caudal portion of the fluid flow guide that atleast partially covers the caudal structural member is shaped so as todefine a caudal bulge that extends radially outward,

deploying the rostral body portion includes deploying the rostral bodyportion such that the rostral bulge extends radially outward against andsealingly contacts a rostral portion of an abdominal aortic aneurysm inthe aorta when the stent-graft assumes the radially-expanded state, and

deploying the caudal body portion includes deploying the caudal bodyportion such that the caudal bulge extends radially outward against andsealingly contacts a caudal portion of the abdominal aortic aneurysm inthe aorta when the stent-graft assumes the radially-expanded state.

For some applications, a portion of the caudal structural member isflared radially outward at a caudal end thereof, when the stent-graftassumes the radially-expanded state, and deploying the caudal bodyportion includes deploying the caudal body portion such that the flaredportion is adjacently caudal to an aorto-iliac bifurcation.

For some applications, the method further includes: introducing via afirst iliac artery to a second iliac artery a bi-iliac self-expandablestent in a radially-compressed state so that the bi-iliac stent subtendsthe aorto-iliac bifurcation; deploying the bi-iliac stent to aradially-expanded state; and introducing and inflating a balloon in thebi-iliac stent.

For some applications, the stent-graft further includes an iliacextension stent, which is connected to an element selected from thegroup consisting of: a caudal end of the caudal body portion, or thecaudal structural member within the caudal body portion, and furtherincluding deploying the iliac extension stent in a first one of theiliac arteries after deploying the caudal body portion into the aorta.For some applications, the iliac extension stent is shaped such that arostral portion thereof defines a lateral opening therethrough, definedby a discontinuity of stents cells of the extension stent, subtending anarc angle of more than 320 degrees. For some applications, the methodfurther includes: introducing a bi-iliac self-expandable stent via thedeployed iliac extension stent to a second one of the iliac arteries ina radially-compressed state such that the bi-iliac stent subtends anaorto-iliac bifurcation; deploying the bi-iliac to a radially-expandedstate; and introducing and inflating a balloon in the bi-iliac stent.

The present invention will be more fully understood from the followingdetailed description of embodiments thereof, taken together with thedrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are schematic illustrations of an endovascularstent-graft, in accordance with an application of the present invention;

FIG. 3 is a schematic illustration of a bifurcated configuration of theendovascular stent-graft of FIGS. 1 and 2, in accordance with anapplication of the present invention;

FIGS. 4A-D are schematic illustrations of an exemplary method ofdeploying the endovascular stent-graft of FIGS. 1 and 2 in a rostral endof an abdominal aortic aneurysm, in accordance with an application ofthe present invention;

FIG. 4E schematically illustrates two of the stent-grafts of FIGS. 1 and2 in their respective fully deployed states, in accordance with anapplication of the present invention;

FIGS. 5A-B are schematic illustrations of an endovascular stent-graftcomprising a foldable skirt, in accordance with an application of thepresent invention;

FIGS. 6A-D are schematic illustrations of an exemplary method ofdeploying the endovascular stent-graft of FIGS. 5A-B, in accordance withan application of the present invention;

FIGS. 7A-C are schematic illustrations of an endovascular prosthesiscomprising a plurality of tissue engagement members, in accordance withrespective applications of the present invention;

FIGS. 8A and 8B are schematic illustrations of the endovascularprosthesis of FIG. 7C, immediately following its deployment in therostral portion of an aortic aneurysm and a few weeks following itsdeployment, respectively, in accordance with an application of thepresent invention;

FIGS. 9A-B are schematic illustrations of a doubly-flared endovascularstent-graft prosthesis, in accordance with an application of the presentinvention;

FIGS. 9C and 9D are schematic illustrations of the prosthesis of FIGS.9A-B deployed in the vicinity of the renal arteries, in accordance withrespective applications of the present invention;

FIGS. 10A-B are schematic illustrations of a self-expandinglumen-engagement prosthesis member, in accordance with respectiveapplications of the present invention;

FIGS. 11A-C are schematic illustrations of a self-expandableendovascular sealing stent-graft, in accordance with an application ofthe present invention;

FIGS. 12A-D are four schematic axial cross-sections of the stent-graftof FIGS. 11A-C in the abdominal aorta in a vicinity of the renalarteries, in accordance with an application of the present invention;

FIG. 13 is a schematic illustration of a unilumen endovascularstent-graft, in accordance with an application of the present invention;

FIGS. 14A-E are schematic illustrations of an exemplary method ofdeploying the endovascular stent-graft of FIG. 13 in an aneurysmaticabdominal aorta, in accordance with an application of the presentinvention;

FIGS. 15A-C are schematic illustrations of the unilumen endovascularstent-graft of

FIG. 13 coupled to a uni-iliac self-expandable extension stent, inaccordance with respective applications of the present invention;

FIG. 16 is a schematic illustration of a configuration of the unilumenendovascular stent-graft of FIG. 13 further comprising a plurality ofcircumferentially-disposed, axially-oriented engagement members, inaccordance with an application of the present invention;

FIG. 17 is a schematic illustration of the configuration of thestent-graft of FIG. 16 deployed in an aneurysmatic aorta, in accordancewith an application of the present invention;

FIG. 18 is a schematic illustration of a configuration of the unilumenendovascular stent-graft of FIG. 13 further comprising a self-expandableuni-iliac extension stent, in accordance with an application of thepresent invention;

FIG. 19 is a schematic illustration of the unilumen endovascularstent-graft of FIG. 13 coupled to a uni-iliac self-expandable stent, inaccordance with an application of the present invention;

FIGS. 20A-B are schematic illustrations of a configuration of theunilumen endovascular stent-graft of FIG. 13 further comprising at leasttwo iliac engagement members, in accordance with an application of thepresent invention; and

FIGS. 21A-B are schematic illustrations of the configuration of theunilumen stent-graft of FIGS. 20A-B deployed in an aneurysmatic aorta,in accordance with an application of the present invention.

DETAILED DESCRIPTION OF APPLICATIONS Endovascular Stent-Graft Having aBulge

FIGS. 1 and 2 are schematic illustrations of an endovascular stent-graft5, in accordance with an application of the present invention.Endovascular stent-graft 5 is configured to initially be positioned in adelivery catheter in a radially-compressed state, as describedhereinbelow with reference to FIG. 4A, and to assume a radially-expandedstate upon being deployed from the delivery catheter, as describedhereinbelow with reference to FIGS. 4B-E. FIGS. 1 and 2 show theendovascular stent-graft in the radially-expanded state. For someapplications, the stent-graft, and other stent-grafts and prosthesesdescribed herein, are heat-set to assume the radially-expanded state.

Stent-graft 5 comprises a structural member 10 and a fluid flow guide16. FIG. 1 shows only the structural member, while FIG. 2 shows thefluid flow guide fixed to the structural member. Structural member 10comprises a plurality of structural stent elements 15. For someapplications, at least some of, e.g., all of, the structural stentelements are interconnected (as shown in the figures), while for otherapplications, at least a portion of, e.g., all, of the structural stentelements are not interconnected (configuration not shown). For someapplications, a rostral-most first portion of structural stent elements15 define a plurality of anchoring elements 7 that extend radiallyoutwardly, and, optionally, rostrally, when the stent-graft assumes theradially-expanded state, as shown in FIGS. 1 and 2. The anchoringelements anchor the stent-graft to the vascular wall, helping preventdislodgement. Optionally, one or more of anchoring elements 7 are shapedso as to define respective barbs 37. (As used in the presentapplication, including in the claims, a “barb” means an element havingat least one free sharp end, which is sharp enough to enter the aorticwall. The element does not necessarily define a sharp projectionextending backward from the sharp end for preventing easy extraction.) Asecond portion of structural stent elements 15 define a stent body 8when the stent-graft assumes the radially-expanded state. The secondportion of members 15 are typically coupled to the first portion ofmembers 15, and immediately caudal to the first portion. Structuralmember 10 has a rostral end 11 and a caudal end 12, between which stentbody 8 is positioned. For some applications, structural member 10comprises a metal. Alternatively or additionally, the structural membercomprises a self-expanding material. Alternatively or additionally, thestructural member comprises a super-elastic alloy, such as Nitinol.

As shown in FIG. 2, fluid flow guide 16 comprises at least onebiologically-compatible substantially fluid-impervious flexible sheet,which is coupled to stent body 8, either outside or within the body,such as by stitching, and covers either an external or an internalsurface of at least a portion of the stent body. (FIG. 2 shows a cut-outportion of fluid flow guide 16 to better show structural stent elements15 within the fluid flow guide.) Fluid flow guide 16 has a rostral end17 and a caudal end 18. Fluid flow guide 16 typically covers the entirestent body, in order to define a fluid flow path through the body. Theflexible sheet may comprise, for example, a polymeric material (e.g.,polytetrafluoroethylene), a textile material (e.g., polyethyleneterephthalate (PET)), natural tissue (e.g., saphenous vein or collagen),or a combination thereof. Optionally, caudal end 12 of structural member10 extends beyond a caudal end of stent body 8 and caudal end 18 offluid flow guide 16, for example, slightly beyond, as shown in FIG. 2;stent body 8 thus does not include a caudal-most portion of structuralstent elements 15 that extend caudally beyond caudal end 18 of fluidflow guide 16. For some applications, rostral end 17 of fluid flow guide16 is disposed within 1-4 cm of rostral end 11 of structural member 10.For some applications, caudal end 18 of the fluid flow guide is disposedwithin 0.5-2 cm of caudal end 12 of the structural member.

When the stent-graft assumes the radially-expanded state, fluid flowguide 16 is shaped so as to define radially-diverging andradially-converging portions 13 and 19, typically within 10 cm of arostral end of the stent body. The portions together define a bulge 20that extends radially outward, which has a greatest cross-sectional areathat is equal to at least 120%, e.g., at least 160%, of across-sectional area of a narrowest portion 17 of the stent-graftrostral to the bulge (the stent-graft may have an even narrower portioncaudal to the bulge). When the stent-graft is deployed in the aorta,bulge 20 extends radially outward against a rostral portion of theaortic aneurysm, thereby helping prevent a current or a future type Iendoleak. Typically, when the stent-graft assumes the radially-expandedstate, a site on bulge 20 that has the greatest cross-section area iswithin 5 cm, at least 2 cm from, and/or between 2 and 5 cm of rostralend 17 of fluid flow guide 16.

Typically, the stent-graft is configured such that bulge 20 expandsradially as the rostral end of the aneurysm enlarges post-implantation,in order to maintain a tight seal with the wall of the aorta, therebypreventing current or future type I endoleaks. At the same time, thestent-graft is configured to apply a radially-outward force that issufficient to cause the bulge to expand with the aortic wall, butinsufficient to itself cause expansion of the aortic wall. For someapplications, structural member 10 is configured such that, when thestent-graft assumes the radially-expanded state, bulge 20 applies aradially-outward force that is less than a radially-outward forceapplied by anchoring elements 7. For example, the radially-outward forceapplied by the bulge may be at least 25%, no more than 50%, and/orbetween 25% and 50% of the radially-outward force applied by theanchoring elements. For example, the anchoring elements may beconfigured to apply more than half a newton, no more than five newton,or between one half a newton and five newton to the aortic wall (or moregenerally, if placed within a cylinder having a diameter of 2.5 cm).

Typically, a first subset 22 of structural stent elements 15 of stentbody 8 are configured to cause fluid flow guide 16 to define bulge 20,when the stent-graft assumes the radially-expanded state. For someapplications, a second subset 23 of structural stent elements 15 ofstent body 8 are not configured to cause fluid flow guide 16 to definebulge 20, when the stent-graft assumes the radially-expanded state. Thestructural stent elements of first subset 22 at least partially overlapthe structural stent elements of second subset 23 lengthwise along thestent body, and the structural stent elements of first subset 22 arepositioned generally radially outward from the structural stent elementsof second subset 23 when the stent-graft assumes the radially-expandedstate. For some applications, structural stent elements 15 comprise ametal, and, when the stent-graft assumes the radially-compressed state,structural stent elements 15 of first subset 22 contact at least aportion of structural stent elements 15 of second subset 23. Typically,structural stent elements 15 of first subset 22 are interconnected.Alternatively or additionally, structural stent elements 15 of secondsubset 23 are interconnected.

For some applications, the structural stent elements of first subset 22radially converge with the structural stent elements of second subset 23at respective rostral ends of the subsets (as shown in the figures),and/or at respective caudal ends of the subsets (configuration notshown). For some applications, a third subset 25 of structural stentelements 15 of stent body 8 connect structural stent elements 15 offirst subset 22 with the structural stent elements of second subset 23,and thus as communicating support members. Optionally, when thestent-graft assumes the radially-expanded state, structural stentelements 15 of third subset 25 are substantially radially oriented.

For some applications, when the structural member assumes theradially-expanded state, structural stent elements 15 of first subset 22are concentric with the structural stent elements of second subset 23.For some applications, first and second subsets 22 and 23 are mutuallyexclusive, i.e., do not contain any common, mutual structural stentelements 15. For other applications, the first and second subsets shareat least one of the structural members, i.e., at least one of thestructural members is a member of both the first and second subsets. Forsome applications, third subset 25 is mutually exclusive with both firstand second subsets 22 and 23, while for other applications, the thirdsubset shares at least one structural member with the first subsetand/or the second subset.

Typically, first subset 22 (which causes fluid flow guide 16 to definebulge 20) has a lower spring coefficient than second subset 23. Morespecifically, assume a radial force were to be applied by two rigidcircular disks to two respective regions on stent body 8, respectivelycentered at: (1) a point A of first subset 22 that is furthest from acentral longitudinal axis of the stent body, and (2) a point B of secondsubset 23 that is axially aligned with point A, wherein each of thecircular disks has a radius equal to 50% of a radius of stent body 8 atpoint A. For some applications, a spring coefficient of first subset 22,measured during application of the radial force at the region aroundpoint A, is at least 20% less than a spring coefficient of second subset23, measured during application of the radial force at the region aroundpoint B. For some applications, a spring coefficient of first subset 22,measured during application of a radial force at the region around pointA, is at least 20% less than a spring coefficient of rostral anchoringelements 7, measured during application of the radial force at a regionaround a point of the anchoring elements that is furthest from the axisof the stent body.

For some applications, when the stent-graft assumes theradially-expanded state, structural stent elements 15 of second subset23 (which do not cause the fluid flow guide to define the bulge) areshaped so as to define a substantially tubular structure, e.g., aconstant diameter cylinder, or a flared cylinder, which is configured toretain a generally constant diameter even as the bulge expands radiallyoutward over time post-implantation. As used in the present application,including in the claims, “tubular” means having the form of an elongatedhollow object that defines a conduit therethrough. A “tubular” structuremay have varied cross-sections therealong, and the cross-sections arenot necessarily circular. For example, one or more of the cross-sectionsmay be generally elliptical but not circular, or circular.

For some applications, when the stent-graft assumes theradially-expanded state, structural stent elements 15 of first subset 22(which cause fluid flow guide 16 to define bulge 20) are shaped so as todefine a plurality of arms 24 that extend radially outward, and areconfigured to cause fluid flow guide 16 to define bulge 20. Typically,when the stent-graft assumes the radially-expanded state, arms 24 extendradially outward in a caudal direction, as shown in FIGS. 1 and 2.Alternatively, the arms extend radially outward in a rostral direction.

For some applications, structural stent elements 15 of first subset 22define an external structural lumen, which is disposed radially outwardof an internal structural lumen defined by structural stent elements 15of second subset 23 when the stent-graft assumes the radially-expandedstate. The external structural lumen at least partially overlaps theinternal structural lumen lengthwise along the stent body. (As used inthe present application, including in the claims, a “structural lumen”means a passageway defined by structural stent elements 15, even thoughthe passageway does not necessarily define a fluid flow path.) Thediameter of body portion 8 of the external structural lumen is mostlylarger than the diameter of the body portion of the internal structurallumen.

For some applications, when the stent-graft assumes theradially-expanded state, structural stent elements 15 of first subset 22are grouped into a plurality of axially-disposed arrays, each of whicharrays generally circumscribes at least a 360-degree arc. Each of thearrays is substantially morphologically deformable independently of theaxially adjacent arrays. As a result, deformation of each of the arrayshas minimal impact on the axially adjacent arrays, providing the bulgewith good surface conformation to the end of the aneurysm, therebysealing the aneurysm end. For some applications, at least a portion(e.g., all) of the arrays are structurally connected to the axiallyadjacent arrays, by connecting stent elements. These connections providesome columnar strength to first subset 22. For other applications, atleast a portion (e.g., none) of the arrays are not structurallyconnected to the axially adjacent arrays, such that at least a portionof the arrays serve as bare crowns.

FIG. 3 is a schematic illustration of a bifurcated configuration ofstent-graft 5, in accordance with an application of the presentinvention. In this configuration, stent body 8 is bifurcated, such thatthe stent body is shaped so as to define two branches, which definerespective lumens. (The branches typically have differing lengths, as isknown in the art for conventional stent-grafts.) Alternatively, when thestent-graft assumes the radially-expanded state, the caudal end of thestructural member and the caudal end of the fluid flow guide togetherdefine a single lumen, as shown in FIG. 2.

FIGS. 4A-D are schematic illustrations of an exemplary method ofdeploying endovascular stent-graft 5 in a rostral end 35 of an abdominalaortic aneurysm 34, using an endovascular stent-graft delivery tool 4,in accordance with an application of the present invention. As shown inFIG. 4A, delivery tool 4 typically comprises a delivery catheter 30, adistal tip 31, and a guidewire 33. In order to implant endovascularstent-graft 5, the stent-graft is transvascularly (typicallypercutaneously) introduced into the aorta via one of iliac arteries 36,while the stent-graft is positioned in delivery catheter 30 in theradially-compressed state. Delivery catheter 30 and distal tip 31 areadvanced over guidewire 33 until the distal tip is positioned slightlybelow renal arteries 32.

FIG. 4B shows rostral end 11 of structural member 10 in an early stageof release from delivery catheter 30. The stent-graft is positioned suchthat rostral anchoring elements 7 are disposed rostrally to renalarteries 32.

FIG. 4C shows the stent-graft in a subsequent phase of its deploymentfrom delivery catheter 30, in which bulge 20 is disposed in rostral end35 of aneurysm 34, and sealingly contacts the aortic wall, therebypreventing or reducing the risk of a current or a future a type Iendoleak.

FIG. 4D shows the stent-graft in its fully deployed state, afterdelivery tool 4 has been removed from the subject's body. At least oneadditional primary stent-graft may be coupled to the caudal end of thestent-graft, such as using techniques described hereinbelow withreference to FIG. 9D, mutatis mutandis (for clarity of illustration, notshown in FIG. 4D). The primary stent-graft is structurally coupled tosecond subset 23 of structural elements 15, which do not define thebulge, and may define the internal structural lumen. Alternatively, atleast one additional primary stent-graft may be integral to thestent-graft, such that the stent-graft is sufficiently long to reach theaorta-iliac bifurcation.

Bulge 20 exerts a force against the wall of the aorta, labeled in FIG.4D as force vector F₂. Force vector F₂ has both vertical and horizontalcomponents F₂y and F₂x. Similarly, anchoring elements 7 exert a forceagainst the wall of the aorta, labeled as force vector F₁. Force vectorF₁ has both vertical and horizontal components F₁y and F₁x. The verticalforce components F₁y and F₂y are directed towards one another, so as toaxially pinch the aortic wall between the neck of the aneurysm and therostral end of the aneurysm, thereby enhancing the anchoring of thestent-graft to the wall of the aorta, and reducing the likelihood ofloosening of the prosthesis which may result in a type I endoleak.

FIG. 4E schematically illustrates two of stent-grafts 5A and 5B in theirrespective fully deployed states, in accordance with an application ofthe present invention. A first stent-graft 5A has its bulge 20A disposedin rostral end 35 of aneurysm 34, thereby preventing a current or afuture a type I endoleak. A second stent-graft 5B is oriented in anaxial direction opposite to that of first stent-graft 5A, and has itsbulge 20B disposed in a caudal end 14 of aneurysm 34, near thebifurcation of the aorta into two iliac arteries 36, thereby preventinga current or a future a type endoleak at the aorto-iliac bifurcation.The caudal ends of the stent-grafts are deployed one inside the other,in order to provide fluid-tight coupling of the stent-grafts with eachother. Optionally, anchoring elements 7 of second stent-graft 5B arepositioned to engage an aorta-iliac bifurcation.

Endovascular Stent-Graft Having a Foldable Skirt

FIGS. 5A-B are schematic illustrations of an endovascular stent-graft 39comprising a foldable skirt 42, in accordance with an application of thepresent invention. Endovascular stent-graft 39 is configured toinitially be positioned in a delivery catheter in a radially-compressedstate, as described hereinbelow with reference to FIG. 6A, and to assumea radially-expanded state upon being deployed from the deliverycatheter, as described hereinbelow with reference to FIGS. 6B-D. FIGS.5A-B show the endovascular stent-graft in the radially-expanded state.

Stent-graft 39 comprises a structural member 40 and a fluid flow guide41. Structural member 40 comprises a plurality of structural stentelements 46. For some applications, at least some of, e.g., all of, thestructural stent elements are interconnected (as shown in the figures),while for other applications, at least a portion of, e.g., all of, thestructural stent elements are not interconnected (configuration notshown). (The structural stent elements, other than those that defineanchoring elements 47, are not directly visible in the figures; however,the positioning of the structural stent elements is indicated by thestitching that couples fluid flow guide 41 to the flexible sheet of theskirt to the structural stent elements. This is also the case for otherconfigurations shown with stitching in some of the other figures.) Forsome applications, a rostral-most first portion of structural stentelements 46 define a plurality of anchoring elements 47 that extendradially outwardly and rostrally when the stent-graft assumes theradially-expanded state, as shown in FIGS. 5A-B. The anchoring elementsanchor the stent-graft to the vascular wall, helping preventdislodgement. Optionally, one or more of anchoring elements 47 areshaped so as to define respective barbs 37. A second portion ofstructural stent elements 46 define a tubular body 38 when thestent-graft assumes the radially-expanded state. The second portion ofmembers 46 are typically coupled to the first portion of members 46, andimmediately caudal to the first portion.

Fluid flow guide 41 comprises at least one biologically-compatiblesubstantially fluid-impervious flexible sheet, which is coupled totubular body 38, either outside the body or within the body, such as bystitching, and covers either an external or an internal surface of atleast a portion of the tubular body. Fluid flow guide 41 typicallycovers the entire tubular body, in order to define a fluid flow paththrough the body. The flexible sheet may comprise, for example, apolymeric material (e.g., polytetrafluoroethylene), a textile material(e.g., polyethylene terephthalate (PET)), natural tissue (e.g.,saphenous vein or collagen), or a combination thereof. Optionally, acaudal end of structural member 40 extends beyond a caudal end oftubular body 38 and a caudal end of fluid flow guide 41, for example,slightly beyond, as shown in FIGS. 5A-B; tubular body 38 thus does notinclude a caudal-most portion of structural stent elements 46 thatextend caudally beyond the caudal end of fluid flow guide 41. For someapplications, a caudal end of the fluid flow guide is disposed within 5cm of, at least 2 cm from, and/or between 2 and 5 cm of a caudal end ofthe structural member.

Stent-graft 39 further comprises rostrally-positioned foldable skirt 42,which comprises at least one biologically-compatible substantiallyfluid-impervious flexible sheet 54. (FIG. 5A shows a cut-out portion ofskirt 42 to better show anchoring elements 47.) Skirt 42 extends fromstructural member 40 at a circumferential juncture 48 between anchoringelements 47 and tubular body 38, and terminates in a peripheral edge 44.Peripheral edge 44 has a greater circumference than that ofcircumferential juncture 48 when the stent-graft assumes theradially-expanded state. For example, when the stent-graft assumes theradially-expanded state, the circumference of circumferential juncture48 may be at least 10 cm, no more than 18 cm, and/or between 10 and 18cm, and the circumference of peripheral edge 44 may at least 120%, nomore than 150%, and/or between 120% and 150% of the circumference ofcircumferential juncture 48. Typically, the circumference of peripheraledge 44 is greater than a circumference of all other elements of thestent-graft, when the stent-graft assumes the radially-expanded state.The skirt is typically sealingly coupled to a rostral end of fluid flowguide 41 around the entire circumferential juncture. Typically, theperipheral edge has a non-traumatic shape, e.g., rounded, so as tominimize tissue trauma when the tissue applies the caudally orientedforce, as described hereinbelow with reference to FIG. 6C.

Flexible sheet 54 of skirt 42 is typically supported by a scaffold 43,which typically extends from at least a portion of juncture 48 to atleast a portion of peripheral edge 44 of the skirt. For someapplications, the juncture comprises a pivot, to which the scaffold isrotatably coupled so as to allow the skirt to transition from extendingrostrally to extending caudally, as described below. For someapplications, scaffold 43 comprises a self-expanding material, and/or asuper-elastic alloy, such as Nitinol.

FIG. 5A shows skirt 42 extending rostrally from circumferential juncture48. The skirt assumes this position when the stent-graft is initiallypositioned in the delivery catheter, as described hereinbelow withreference with reference to FIG. 6A, and retains this position initiallyupon being deployed from the catheter, as described hereinbelow withreference to FIG. 6B. In this position, skirt 42 is positioned radiallysurrounding anchoring elements 47. This rostrally-extending positionfacilitates low-profile mounting of the endovascular stent-graft in theradially-compressed state within the delivery catheter.

FIG. 5B shows skirt 42 extending caudally from circumferential juncture48, in order to facilitate sealing of blood leakage around thestent-graft when it assumes the radially-expanded state. The skirtassumes this position upon application of a caudally-directed force toperipheral edge 44 of the skirt after deployment of the stent-graft fromthe delivery catheter, as described hereinbelow with reference to FIG.6C.

FIGS. 6A-D are schematic illustrations of an exemplary method ofdeploying endovascular stent-graft 39 using endovascular stent-graftdelivery tool 4, described hereinabove with reference to FIG. 4A, inaccordance with an application of the present invention. As shown inFIG. 6A, in order to implant stent-graft 39, the stent-graft istransvascularly (typically percutaneously) introduced into the aorta viaone of iliac arteries 36, while the stent-graft is positioned indelivery catheter 30 in the radially-compressed state. Delivery catheter30 and distal tip 31 are advanced over guidewire 33 until the distal tipis positioned slightly below renal arteries 32.

As shown in FIG. 6B, at least a portion of skirt 42, includingperipheral edge 44, is deployed from catheter 30, such that theperipheral edge presses radially outward against the wall of the aorta afew centimeters into the aneurysm. Typically, at this stage of themethod, anchoring elements 47 are still held in a radially-compressedstate by distal tip 31 of the delivery tool. Subsequently, juncture 48of skirt 42 is exposed.

As shown in FIG. 6C, rostral advancement of the partially expanded skirtcauses the wall of the aorta to apply a caudally-directed force toperipheral edge 44 of the skirt, causing the skirt to fold back, i.e.,invert, in a caudal direction. The skirt extends caudally from thejuncture in order to facilitate sealing of blood leakage around thestent-graft when it assumes the radially-expanded state. Circumferentialjuncture 48 between skirt 42 and tubular body 38 is disposed rostrallyto peripheral edge 44 of skirt 42. Alternatively or additionally, thecaudally-directed force is applied by one or more elongated members(e.g., cords) that are coupled to peripheral edge 44, and are pulledcaudally in order to invert the skirt.

FIG. 6D shows the fully-deployed stent-graft system with skirt 42positioned in rostral end 35 of aneurysm 34, thereby helping prevent acurrent or a future a type I endoleak. Delivery tool 4 is subsequentlyremoved from the subject's body. One or more additional primarystent-grafts may be coupled to the caudal end of the stent-graft, suchas using techniques described hereinbelow with reference to FIG. 9D,mutatis mutandis (for clarity of illustration, not shown in FIG. 6D).Alternatively, one or more additional primary stent-grafts may beintegral to the stent-graft, such that the stent-graft is sufficientlylong to reach the aorto-iliac bifurcation.

Endovascular Stent-Graft Having Tissue Engagement Members

FIGS. 7A-C are schematic illustrations of an endovascular prosthesis 49comprising a plurality of tissue engagement members 52, in accordancewith respective applications of the present invention. Endovascularprosthesis 49 is configured to initially be positioned in a deliverycatheter in a radially-compressed state, such as described hereinabovewith reference to FIGS. 4A and 6A for stent-grafts 5 and 39,respectively, mutatis mutandis. Prosthesis 49 is configured to assume aradially-expanded state upon being deployed from the delivery catheter,such as described hereinabove with reference to FIGS. 4B-E and 6B-D forstent-grafts 5 and 39, respectively, mutatis mutandis. FIGS. 7A-C showthe endovascular prosthesis in the radially-expanded state.

Endovascular prosthesis 49 comprises a structural member 50, a pluralityof circumferentially disposed tissue engagement members 52, and aplurality of communicating members 53 that respectively connectstructural member 50 to the tissue engagement members 52. For someapplications, the prosthesis further comprises a fluid flow guide 51,similar to the fluid flow guides described hereinabove with reference toFIGS. 2 and 5A-B. Structural member 50 comprises a plurality ofstructural stent elements 57. For some applications, at least some of,e.g., all of, the structural stent elements are interconnected (as shownin the figures), while for other applications, a portion of, e.g., allof, the structural stent elements are not interconnected (configurationnot shown). For some applications, a rostral-most first portion ofstructural stent elements 57 define a plurality of anchoring elements 56that extend radially outwardly (and optionally rostrally or caudally)when the stent-graft assumes the radially-expanded state, as shown inFIGS. 7A-C. The anchoring elements immediately anchor the prosthesis tothe vascular wall upon deployment, helping prevent dislodgement.Optionally, one or more of anchoring elements 56 are shaped so as todefine respective barbs 71. A second portion of structural stentelements 57 define a stent body 74 when the stent-graft assumes theradially-expanded state. The second portion of members 57 are typicallycoupled to the first portion of members 57, and immediately caudal tothe first portion. For some applications, structural member 50 comprisesa metal. Alternatively or additionally, the structural member comprisesa self-expanding material. Alternatively or additionally, the structuralmember comprises a super-elastic alloy, such as Nitinol.

Tissue engagement members 52 are disposed (typically, circumferentially)externally to stent body 74 when the prosthesis assumes theradially-expanded state. Communicating members 53 are generallyradially-oriented when the prosthesis assumes the radially-expandedstate. For example, when the prosthesis assumes the radially-expandedstate, the communicating members may define an angle of between 20 and90 degrees, such as between 50 and 70 degrees, with an external surfaceof stent body 74. Typically, the tissue engagement members are blunt,i.e., are not shaped so as to define any sharp elements that extendgenerally radially outward with respect to the stent body, such asspikes or barbs. As a result, the tissue engagement members cause lowtrauma to the wall of the aorta, and typically do not pierce the wall,thus allowing flexibility during deployment of the prosthesis. Thetissue engagement members are typically heat-set to outwardly radiallyprotrude, such that several weeks after placement of the prosthesis, thetissue engagement members become embedded in the wall of the aorta,thereby helping hold the prosthesis in place. The tissue engagementmembers typically have a larger surface area than conventional barbs,such as a surface area of at least 0.5 mm2, no more than 8 mm2, and/orbetween 0.5 and 8 mm2. Typically, each of the tissue engagement membersextends in one or more directions generally parallel to a surface ofstent body 74. Respective distances between the surface of stent body 74and all locations of each of the tissue engagements members typicallyvary by less than 30%. For some applications, prosthesis 49 furthercomprises a plurality of connecting elements, which couple at least aportion of the tissue engagement members to respective adjacent ones ofthe tissue engagement members (configuration not shown).

For some applications, when the prosthesis assumes the radially-expandedstate, a spring coefficient of each of the communicating members 53,measured during application of a radial force by a rigid circular disk,is at least 20% less than a spring coefficient of stent body 74,measured during application of the radial force by disk at a regionaround point on the stent body at which the communicating member isconnected, wherein the disk has a radius equal to 50% of a radius ofstent body at the point. This lesser spring coefficient may facilitategradual penetration of the communicating members into adjacent vascularwall tissue, while allowing tight circumferential conformity between thestent body and the adjacent vascular wall tissue. For some applications,when the prosthesis assumes the radially-expanded state, the tissueengagement members radially protrude a distance of at least 1 mm, nomore than 4 mm, and/or between 1 and 4 mm from the stent body.

In the configuration shown in FIG. 7A, tissue engagement members 52 aregenerally circumferentially arcuate and extend laterally around stentbody 74. For some applications, the tissue engagement members aredisposed as a circumferential and axial array around stent body 74.

In the configuration shown in FIG. 7B, tissue engagement members 52 aregenerally linear and extend axially along the stent body. For someapplications, the tissue engagement members are arranged as an axialarray along the stent body.

In the configuration shown in FIG. 7C, tissue engagement members 52 arepolygonal, e.g., diamond-shaped, similar to the shape of standard stentclosed cells.

FIGS. 8A and 8B are schematic illustrations of endovascular prosthesis49 with the configuration of FIG. 7C, immediately following itsdeployment in the rostral portion of aortic aneurysm 34 and a few weeksfollowing its deployment, respectively, in accordance with anapplication of the present invention. Prosthesis 49 is typicallytransvascularly (typically percutaneously) introduced into the aortausing delivery tool 4, such as described hereinabove with reference toFIG. 4A, mutatis mutandis. In the state shown in FIG. 8A, tissueengagement member 52 is pressing against aortic wall 55, but not yetbeen incorporated into the aortic wall. In the state shown in FIG. 8B,the tissue engagement member and communicating member have beenincorporated into aortic wall 55.

Doubly-Flared Endovascular Stent-Graft

FIGS. 9A-B are schematic illustrations of a doubly-flared endovascularstent-graft prosthesis 59, in accordance with an application of thepresent invention. Endovascular prosthesis 59 is configured to initiallybe positioned in a delivery catheter in a radially-compressed state,such as described hereinabove with reference to FIGS. 4A and 6A forstent-grafts 5 and 39, respectively, mutatis mutandis. Prosthesis 59 isconfigured to assume a radially-expanded state upon being deployed fromthe delivery catheter, such as described hereinabove with reference toFIGS. 4B-E and 6B-D for stent-grafts 5 and 39, respectively, mutatismutandis. FIGS. 9A-B show the endovascular prosthesis in theradially-expanded state.

Endovascular prosthesis 59 comprises a structural member 60. When theprosthesis assumes the radially-expanded state, structural member 60 isshaped so as to define:

-   a flared rostral portion 61, which flares radially outward in a    rostral direction (i.e., a cross-sectional area of portion 61    increases as one moves in the rostral direction);-   a flared caudal portion 63, which flares radially outward in a    caudal direction (i.e., a cross-sectional area of portion 63    increases as one moves in the caudal direction); and-   optionally, a generally constant-diameter body portion 62, which is    disposed longitudinally between the flared rostral and caudal    portions, and has a diameter that varies by less than 15% along an    entire length thereof, such as by less than 10%.

For some applications, structural member 60 comprises a plurality ofstructural stent elements 67. For some applications, at least some of,e.g., all of, the structural stent elements are interconnected (as shownin the figures), while for other applications, at least a portion of,e.g., all of, the structural stent elements are not interconnected(configuration not shown). For some applications, flared rostral portion61 comprises a plurality of anchoring elements 69 that extend radiallyoutwardly (and optionally rostrally or caudally) when the prosthesisassumes the radially-expanded state, as shown in FIGS. 9A-B. Theanchoring elements help anchor the prosthesis to the vascular wall upondeployment, helping prevent dislodgement. Optionally, one or more ofanchoring elements 69 are shaped so as to define respective barbs 68.For some applications, structural member 60 comprises a metal.Alternatively or additionally, the structural member comprises aself-expanding material. Alternatively or additionally, the structuralmember comprises a super-elastic alloy, such as Nitinol. For someapplications, the structural member is woven or braided.

For some applications, a spring coefficient of flared caudal portion 63,measured during application of a radial force by a rigid circular diskat a region centered at a first point on the flared caudal portion thatis furthest from a central longitudinal axis of the prosthesis, is (a)at least 20% less than a spring coefficient of body portion 62, measuredduring application of the radial force by the disk at a region centeredat a second point on the body portion that is furthest from the axis ofthe prosthesis, and/or (b) at least 20% less than a spring coefficientof flared rostral portion 61, measured during application of the radialforce by the disk at a region centered at a third point on the flaredrostral portion that is furthest from the axis of the prosthesis,wherein the circular disk has a radius equal to 50% of a radius of theprosthesis at the first point. The low spring coefficient helps flaredcaudal portion 63 to maintain a tight seal with the wall of the aorta,thereby preventing current or future type I endoleaks. At the same time,flared caudal portion is configured to apply a radially-outward forcethat is sufficient to expand with the aortic wall, but insufficient toitself cause expansion of the aortic wall.

For some applications, the prosthesis further comprises a fluid flowguide 66, which comprises at least one biologically-compatiblesubstantially fluid-impervious flexible sheet, such as describedhereinabove with reference to FIGS. 2 and 5A-B. The fluid flow guide iscoupled to at least body portion 62, and additionally to at least aportion of flared caudal portion 63. The portion of the fluid flow guidecoupled to body portion 62 serves to define a lumen for blood flow. Theportion of the fluid flow guide coupled to flared caudal portion 63seals the prosthesis against the aortic wall. This latter portion doesnot necessarily define the lumen, such as for applications in which theprosthesis comprises stent-engagement member 70, as describedhereinbelow with reference to FIG. 9B; for these applications, the lumendefined by the portion of the fluid flow guide coupled to body portion62 is in fluid communication with the lumen defined by thestent-engagement member, and the portion of the fluid flow guide coupledto flared caudal portion 63 provides sealing with the aortic wall ratherthan fluid flow guiding. For some applications, a caudal end of thefluid flow guide is disposed within 4 cm of, at least 1 cm from, and/orbetween 1 and 4 cm of a caudal end of the structural member.

For some applications, an axial length of flared caudal portion 63varies around a circumference of the flared caudal portion. In otherwords, the caudal end of the flared caudal portion is curved, such thatif the prosthesis were to be placed on a flat surface, only a portion ofthe caudal end would touch the surface. For some applications, flaredcaudal portion 63 is externally concave (i.e., concave when viewed fromoutside of the prosthesis), as shown in the figures; for otherapplications, the flared caudal portion is externally convex(configuration not shown). For some applications, the flared caudalportion includes a rostral sub-portion that is externally concave, and amore caudal sub-portion that is externally convex.

For some applications, as can be seen in the cutout of FIG. 9B,prosthesis 59 further comprises a stent-engagement member 70, which,when the prosthesis assumes the radially-expanded state, is generallytubular. Stent-engagement member 70 is configured to be sealinglycoupled to a primary stent-graft, as described hereinbelow withreference to FIG. 9D. Stent-engagement member 70 is disposed at leastpartially within at least one portion selected from the group consistingof: flared caudal portion 63, and body portion 62. Typically, theprosthesis further comprises a biologically-compatible substantiallyfluid-impervious flexible sheet 64, which at least partially covers thestent-engagement member. For some applications, stent-engagement member70 comprises a scaffold 65, which is shown in FIG. 9B partiallyprotruding in a caudal direction from flexible sheet 64. For someapplications, the scaffold comprises a self-expanding material, and/or asuper-elastic alloy, such as Nitinol. For some applications, scaffold 65is constructed as a caudal continuation of body portion 62.

FIGS. 9C and 9D are schematic illustrations of prosthesis 59 deployed inthe vicinity of renal arteries 32, in accordance with respectiveapplications of the present invention. Prosthesis 59 is typicallytransvascularly (typically percutaneously) introduced into the aortausing delivery tool 4, such as described hereinabove with reference toFIG. 4A, mutatis mutandis. The prosthesis is positioned such that (a)flared caudal portion 63 is disposed in rostral end 35 of abdominalaortic aneurysm 34, caudal to both anastomoses of the renal arteries,(b) flared rostral portion 61 is disposed rostral to both of theanastomoses of the renal arteries, and (c) body portion 62, if provided,spans both the anastomoses of the renal arteries. The flare of thecaudal portion seals the prosthesis to the rostral end of the aneurysm,thereby reducing a current or future risk for type I endoleak.

Prosthesis 59 is typically held in place at least by the combination ofthe following forces: (a) the radially outward force of anchoringelements 69, and (b) forces applied by flared rostral portion 61 andflared caudal portion 63. Flared caudal portion 63 exerts a forceagainst the wall of the aorta, labeled in FIG. 9C as force vector F₂.Force vector F₂ has both vertical and horizontal components F₂ y and F₂x. Similarly, flared rostral portion 62, such as anchoring elements 69thereof, exert a force against the wall of the aorta, labeled as forcevector F₁. Force vector F₁ has both vertical and horizontal componentsF₁ y and F₁ x. The vertical force components F₁ y and F₂ y are directedtowards one another, so as to axially pinch the aortic wall between theneck of the aneurysm and the rostral end of the aneurysm, therebyenhancing the anchoring of the stent-graft to the wall of the aorta, andreducing the likelihood of loosening of the prosthesis which may resultin a type I endoleak.

For some applications, a kit is provided that comprises a plurality ofprostheses 59 having different dimensions. One of the prostheses isselected that has a diameter of the body portion that is at least 15%less than a diameter of the aorta between the renal arteries, and has adiameter of a caudal end of the structural member that is at least 20%larger than a diameter of the aorta immediately caudal to a more caudalone of the renal arteries.

Reference is again made to FIG. 9D, which additionally shows a tubularprimary stent-graft 64, a rostral end of which is sealingly coupled tostent-engagement member 70 (not visible in FIG. 9D; see FIG. 9B).Typically, primary stent-graft 64 has a diameter is that 10-15% greaterthan that of the caudal end of stent-engagement member 70. When theprimary stent-graft is inserted into the stent-engagement member, andtransitioned to a radially-expanded state, the outward radial pressureapplied by the primary stent-graft against the inside of thestent-engagement member sealingly couples the primary stent-graft to thestent-engagement member. Primary stent-graft 64 provides afluid-impervious channel to both iliac arteries 36 (for clarity ofillustration, primary stent-graft 64 is not shown extending all the wayto iliac arteries 36; in actual practice, the primary stent-graft doesextend to the iliac arteries). Aortic blood flow is schematicallyindicated by an arrow 74, while arrows 72A and 72B schematicallyindicate blood flowing externally to the prosthesis and into the rightand left renal arteries, respectively. For some applications, primarystent-graft 64 includes a uni-lumen rostral end and bifurcated caudalend, which is configured to be deployed in both iliac arteries.

Barbed Self-Expanding Lumen-Engagement Member

FIGS. 10A-B are schematic illustrations of a self-expandinglumen-engagement prosthesis member 80, in accordance with respectiveapplications of the present invention. Prosthesis member 80 isconfigured to initially be positioned in a delivery catheter in aradially-compressed state, such as described hereinabove with referenceto FIGS. 4A and 6A for stent-grafts 5 and 39, respectively, mutatismutandis. Prosthesis member 80 is configured to assume aradially-expanded state upon being deployed from the delivery catheter,such as described hereinabove with reference to FIGS. 4B-E and 6B-D forstent-grafts 5 and 39, respectively, mutatis mutandis. FIGS. 10A-B showthe prosthesis member in the radially-expanded state.

When prosthesis member 80 assumes the radially-expanded state, theprosthesis member is generally tubular, and defines a centrallongitudinal axis 87. The prosthesis member comprises a plurality ofsupport members 83 distributed around a circumference of the prosthesismember, which are shaped so as to define respective curves havingconcavities that face radially outward. The support members haverespective rostral and caudal ends 81 and 82. Prosthesis member 80further comprises a plurality of rostral barbs 84 and a plurality ofcaudal barbs 85, disposed more caudally than the rostral barbs. When theprosthesis member assumes the radially-expanded state, rostral barbs 84extend caudally and radially outwardly from respective ones of supportmembers 83, and caudal barbs 85 extend rostrally and radially outwardfrom respective ones of the support members. The rostral barbs aretypically only slightly caudally oriented, such as at an angle ofbetween 60 and 85 degrees with respect to the longitudinal axis, such asbetween 50 and 70 degrees, and the caudal barbs are typically onlyslightly rostrally oriented, such as at an angle of between 60 and 85degrees with respect to the longitudinal axis, such as between 50 and 70degrees. Typically, rostral and caudal barbs 84 and 85 are disposed atrostral and caudal ends 81 and 82 of support members 83, respectively.For some applications, prosthesis member 80 comprises an equal number ofrostral and caudal barbs.

The oppositely-oriented rostral and caudal barbs axially pinch tissue ofthe aorta between the barbs, thereby anchoring prosthesis member 80 tothe aorta. The concavity of the support members generally increases theaxial forces applied by the barbs. For some applications, prosthesismember 80 is configured to longitudinally shorten as prosthesis member80 transitions from the radially-compressed state to theradially-expanded state, thereby bringing rostral and caudal ends 81 and82 of the support members 83 closer to each other, as an averagediameter of the structural member increases.

For some applications, prosthesis member 80 is mounted at a rostral endof an endovascular stent-graft 86. For some applications, stent-graft 86comprises a fluid flow guide 88, which comprises at least onebiologically-compatible substantially fluid-impervious flexible sheet.For some applications, prosthesis member 80 is an element of anendovascular stent-graft system, configured to endoluminally treat anaortic aneurysm, such as one of the endovascular stent-graft systemsdescribed herein.

For some applications, the structural member comprises a metal.Alternatively or additionally, the structural member comprisesself-expanding material, and/or a super-elastic alloy, such as Nitinol.Alternatively or additionally, the structural member comprises a braidedor a woven material.

FIG. 10B shows prosthesis member 80 implanted in an aorta, mounted at arostral end of endovascular stent-graft 86. In order to implant theprosthesis member, the prosthesis member is transvascularly (typicallypercutaneously) introduced into the aorta via one of iliac arteries 36,while the prosthesis member is positioned in a delivery catheter in theradially-compressed state. The prosthesis member is transitioned to theradially-expanded state by deploying the prosthesis member from thedelivery catheter in the aorta within 2 cm of, at least 0.5 from, and/orbetween 0.5 and 2 cm of renal arteries 32, such that the prosthesismember engages the aortic wall. For some applications, as shown in FIG.10B, prosthesis member 80 is disposed rostrally to renal arteries 32,while for other application (not shown), the prosthesis member isdisposed caudally to the renal arteries. The prosthesis member istypically sized such that a diameter of structural member 83 when theprosthesis member assumes the radially-expanded state is greater than adiameter of the aorta at sites at which the prosthetic member engagesthe aortic wall. Typically, endovascular stent-graft 86 is positioned soas to engage and seal rostral end 35 of aneurysm 34.

Endovascular Stent-Graft Having Two Rostral Elongated Indentations

FIGS. 11A-C are schematic illustrations of a self-expandableendovascular sealing stent-graft 89, in accordance with an applicationof the present invention. Endovascular stent-graft 89 is configured toinitially be positioned in a delivery catheter in a radially-compressedstate, such as described hereinabove with reference to FIGS. 4A and 6Afor stent-grafts 5 and 39, respectively, mutatis mutandis. Stent-graft89 is configured to assume a radially-expanded state upon being deployedfrom the delivery catheter, such as described hereinabove with referenceto FIGS. 4B-E and 6B-D for stent-grafts 5 and 39, respectively, mutatismutandis. FIGS. 11A-12D show the endovascular stent-graft in theradially-expanded state.

Endovascular stent-graft 89 comprises a structural member 92, whichextends along the entire axial length of the stent-graft, and a fluidflow guide 97, which is coupled to at least a portion of structuralmember. Typically, structural member 92 comprises a plurality ofstructural stent elements. For some applications, at least some of,e.g., all of, the structural stent elements are interconnected (as shownin the figures), while for other applications, at least a portion of,e.g., all of, the structural stent elements are not interconnected(configuration not shown). For some applications, a diameter of thestructural member is between 2.5 and 3 cm, when the stent-graft assumesthe radially-expanded state. For some applications, an axial length ofthe structural member is between 4 and 10 cm, such as between 4 and 7cm, when the stent-graft assumes the radially-expanded state.

For some applications, stent-graft 89 further comprises a plurality ofanchoring elements, which are generally radially oriented when thestent-graft assumes the radially-expanded state (configuration notshown). For example the anchoring elements may be similar to anchoringelement 7, described hereinabove with reference to FIGS. 1 and 2, ortissue engagement members 52, described hereinabove with reference toFIGS. 7A-C.

Fluid flow guide 97 comprises at least one biologically-compatiblesubstantially fluid-impervious flexible sheet, which is coupled tostructural member 92, either outside or within the structural member,such as by stitching, and covers either an external or an internalsurface of at least a portion of the structural member, in order todefine a fluid flow path through the structural member. The flexiblesheet may comprise, for example, a polymeric material (e.g.,polytetrafluoroethylene), a textile material (e.g., polyethyleneterephthalate (PET)), natural tissue (e.g., saphenous vein or collagen),or a combination thereof. For some applications, a rostral end of thefluid flow guide is disposed within 4 cm of, at least 1 cm from, and/orbetween 1 and 4 cm of a rostral end 95 of the structural member. Forsome applications, a caudal end of the fluid flow guide is disposedwithin 2 cm of, at least 0.5 cm from, and/or between 0.5 and 2 cm of acaudal end 96 of the structural member.

As can be seen in FIGS. 11A-C, structural member 92 has a generallytubular shape, e.g., a generally cylindrical shape. The structuralmember is shaped so as to define at least two elongated indentations 90Aand 90B, each of which extends rostrally to rostral end 95 of structuralmember 92, and is tapered in a caudal direction until the indentationconverges with the generally tubular shape of structural member 92.Fluid flow guide 97 covers at least a portion of each of the elongatedindentations. Elongated indentations 90A and 90B serve to direct bloodflow toward the renal arteries. Structural member 92 typically providesan outwardly-directed radial force against the aorta other than at theelongated indentations. The outwardly-directed radial force is typicallyprovided by:

-   a portion of the structural member rostral to the renal arteries;-   a portion of the structural member at the same height as the renal    arteries, but at radial directions other than the elongated    indentations; and-   a portion of the structural member caudal to the renal arteries.    The outwardly-directed force serves to anchor the stent-graft in the    aorta and/or to push the fluid flow guide sealingly against the    aorta, thereby preventing current or future type I endoleaks.

Typically, each of the elongated indentations has an axial length L ofat least 2 cm, no more than 4 cm, and/or between 2 and 4 cm, when thestent-graft assumes the radially-expanded state. For some applications,the structural member comprises a metal. Alternatively or additionally,the structural member comprises a self-expanding material. Alternativelyor additionally, the structural member comprises a super-elastic alloy,such as Nitinol.

FIGS. 11B-C are schematic illustrations of stent-graft 89 positionedcaudal to aortic aneurysm 34 in a vicinity of right and left renalarteries 32A and 32B. The stent-graft is percutaneously andendovascularly introduced into the aorta, via one of iliac arteries,into a vicinity of renal arteries 32A and 32B, while positioned in adelivery catheter in the radially-compressed state. The stent-graft istransitioned to the radially-expanded state by deploying the stent-graftfrom the delivery catheter in the aorta, such that two of elongatedindentations 90A and 90B are radially aligned with renal arteries 32Aand 32B, respectively, with rostral ends of the elongated indentationsrostral to the renal arteries, respectively, and caudal ends of theelongated indentations caudal to the renal arteries, respectively. Toenable this proper rotational orientation, the stent-graft may comprise,for example, one or more radiopaque markers, such as exactly oneradiopaque marker that the physician rotationally aligns with apredetermined anatomical feature. Alternatively or additionally, one ormore radiopaque markers are coupled to the delivery catheter, or anotherportion of the delivery tool.

For some applications, the stent-graft is provided in a kit as one of aplurality of stent-grafts having different, respective angles of offsetbetween two of the elongated indentations (as described hereinbelow withreference to FIG. 12B). In order to select the most appropriatestent-graft from the kit, the physician assesses an angle between renalarteries 32A and 32B, and selects one of the stent-grafts having anangle of offset closest to the assessed angle between the renalarteries. For example, the physician may assess the angel using athree-dimensional reconstruction of a CT angiography or MRA image.

Reference is again made to FIG. 11B. Flow indication arrows 110 and 113schematically indicate blood flow into right and left renal arteries 32Aand 32B, respectively, via right and left elongated indentations 90A and90B, respectively. A flow indication arrow 114 schematically indicatesblood flow through the lumen of stent-graft 89.

FIGS. 12A-D are four schematic axial cross-sections of stent-graft 89 inthe abdominal aorta in a vicinity of renal arteries 32A and 32B, inaccordance with an application of the present invention. Thecross-sections correspond to the planes labeled in FIG. 11C. Rightelongated indentation 90A is shown disposed generally opposing leftelongated indentation 90B. Section XIIA-XIIA (FIG. 12A) is an axialcross-section of the stent-graft rostral to both renal arteries 32A and32B. Section XIIB-XIIB (FIG. 12B) is an axial cross-section of thestent-graft at the level of right renal artery 32A, which is shown to befed blood via right elongated indentation 90A. Section XIIC-XIIC is anaxial cross-section of the stent-graft at the level of left renal artery32B, which is shown to be fed blood via left elongated indentation 90B.Section XIID-XIID is an axial cross-section of the stent-graft at alevel caudal to both renal arteries 32A and 32B.

Typically, a rostral end of each of the elongated indentations spans anarc a (alpha) of between 10 and 40 degrees, such as 15 degrees, asindicated in FIG. 12A, when stent-stent 89 assumes the radially-expandedstate. Typically, when the stent-graft assumes the radially-expandedstate, centers of two of the elongated indentations 90A and 90B areoffset by an angle β (beta) of between 70 and 220 degrees, such asbetween 150 and 170 degrees, e.g., 160 degrees, as measured with respectto a central longitudinal axis 112 of the structural member, asindicated in FIG. 12B. Typically, when the stent-graft assumes theradially-expanded state, a rostral end of each of the elongatedindentations is indented a distance D of between 0.5 and 1 cm from thegenerally tubular shape of the structural member, as indicated in FIG.12D. (It is noted that although FIG. 12D does not actually show therostral end of the elongated indentations, the indicated method ofmeasuring distance D applies equally well the rostral end.)

Unilumen Endovascular Stent-Graft

FIG. 13 is a schematic illustration of a unilumen endovascularstent-graft 200, in accordance with an application of the presentinvention. Endovascular stent-graft 200 is configured to initially bepositioned in a delivery catheter in a radially-compressed state, asdescribed hereinbelow with reference to FIG. 14A, and to assume aradially-expanded state upon being deployed from the delivery catheter,as described hereinbelow with reference to FIGS. 14B-D. FIG. 13 showsthe endovascular stent-graft in the radially-expanded state.

Stent-graft 200 comprises rostral and caudal body portions 210 and 212,which comprise rostral and caudal structural members 214 and 216,respectively. Stent-graft 200 also comprises a middle body portion 218,disposed longitudinally between rostral and caudal body portions 210 and212. Stent-graft 200 further comprises a unilumen fluid flow guide 220.For some applications, middle body portion 218 comprises a middlestructural member, which comprises a plurality of structural stentelements, and which is integrally joined to rostral and caudalstructural members 214 and 216 (not shown in FIG. 13). For someapplications, at least some of, e.g., all of, the structural stentelements are interconnected (as shown in the figures), while for otherapplications, at least a portion of, e.g., all of, the structural stentelements are not interconnected (configuration not shown).Alternatively, middle body portion 218 is not structurally supported byany structural stent elements. Typically, each of rostral and caudalstructural members 214 and 216, and the middle structural member, ifprovided, comprise a plurality of structural stent elements 222. Forsome applications, at least some of, e.g., all of, the structural stentelements are interconnected (as shown in the figures), while for otherapplications, at least a portion of, e.g., all of, the structural stentelements are not interconnected (configuration not shown). For someapplications, the structural members comprise a metal. Alternatively oradditionally, the structural members comprises a self-expandingmaterial. Alternatively or additionally, the structural members comprisea super-elastic alloy, such as Nitinol. For some applications in whichthe middle structural member is provided, at least a portion of themiddle structural member is configured to be axially expandable. Forexample, the middle structural member may comprise one or more generallyhelical wire helices. Optionally, at least one of the helices is aright-handed helix, and at least another of the helices is a left-handedhelix. Alternatively, for example, the structural member may comprise awarp lock knitted structure, comprising, for example, polyester (such asthe Gelseal™ vascular graft, distributed by Vascutek/Terumo, Scotland,UK). Optionally, fluid flow guide 220 is sparsely attached to the middlestructural member.

For some applications, stent-graft 200 further comprises a plurality ofrostral anchoring elements 224 that extend radially outwardly when thestent-graft assumes the radially-expanded state, the anchoring elementsdisposed rostral to rostral body portion 210. The anchoring elementsanchor the stent-graft to the vascular wall, helping preventdislodgement. Optionally, one or more of anchoring elements 224 areshaped so as to define respective barbs 226. Alternatively, for someapplications, stent-graft 200 comprises prosthesis member 80, describedhereinabove with reference to FIGS. 10A-B, which is coupled to therostral end of the stent-graft.

Fluid flow guide 220 comprises at least one biologically-compatiblesubstantially fluid-impervious flexible sheet, which is coupled torostral and caudal structural members 214 and 216, either outside orwithin the structural members, such as by stitching, and at leastpartially covers either an external or an internal surface of both ofthe structural members. A middle portion 228 of fluid flow guide 220extends longitudinally along an entire length of middle body portion218. The flexible sheet may comprise, for example, a polymeric material(e.g., polytetrafluoroethylene), a textile material (e.g., polyethyleneterephthalate (PET)), natural tissue (e.g., saphenous vein or collagen),a polyester, or a combination thereof. Optionally, a rostral end ofrostral structural member 214 extends beyond a rostral end of fluid flowguide 220, for example, slightly beyond, as shown in FIG. 13.Optionally, a caudal end of caudal structural member 216 extends beyonda caudal end of fluid flow guide 220, for example, slightly beyond, asshown in FIG. 13. For some applications, the rostral end of the fluidflow guide is disposed within 4 cm of the rostral end of rostralstructural member 214. For some applications, the caudal end of thefluid flow guide is disposed within 20 cm of the caudal end of caudalstructural member 216.

Fluid flow guide 220 defines a single, non-bifurcated lumen, so as todefine a single fluid flow path through the stent-graft. The singlelumen is configured to entirely span the abdominal aorta between therenal arteries and the aorto-iliac bifurcation, and not to substantiallyextend into the aorto-iliac bifurcation, i.e., to extend into theaorto-iliac bifurcation less than 1 cm, or not at all.

Typically, at least a portion of middle portion 228 of fluid flow guide220 is axially expandable. For example, the portion may be pleated,e.g., accordion-pleated, or may comprise a longitudinally elasticmaterial. For some applications, the stent-graft is configured such thatan axial length of the stent-graft between a rostral end of the rostralbody portion and a caudal end of the caudal body portion is variablebetween a minimum length and a maximum length, the minimum lengthbetween 2 and 5 cm, and the maximum length between 10 and 20 cm. Forsome applications, the stent-graft is configured such that an axiallength of axially-expandable portion of the middle portion is variableup to a maximum length change, which maximum length change is between 2and 20 cm.

For some applications, at least a portion of middle portion 228 of thefluid flow guide 220 is kink-resistant. For example, the portion maycomprise a wrap-knit accordion structure, rings periodically attachedthereto, a wire helix attached thereto, or a stiff material, and/orother techniques known in the art for providing kink-resistance may beused. For some applications, when the stent-graft assumes theradially-expanded state, middle portion 228 of fluid flow guide 220 isgenerally tubular, such as generally cylindrical.

For some applications, when the stent-graft assumes theradially-expanded state, a rostral portion of fluid flow guide 220 thatat least partially covers rostral structural member 214 is shaped so asto define rostral radially-diverging and radially-converging portions230 and 232, which portions together define a rostral bulge 234 thatextends radially outward, which bulge has a greatest cross-sectionalarea that is equal to at least 120% e.g., at least 180%, of across-sectional area of a narrowest portion 236 of the rostral bodyportion rostral to the bulge (the rostral body portion may have an evennarrower portion caudal to the bulge). When the stent-graft assumes theradially-expanded state, a caudal portion of fluid flow guide 220 thatat least partially covers caudal structural member 216 is shaped so asto define caudal radially-diverging and radially-converging portions 240and 242, which portions together define a caudal bulge 244 that extendsradially outward, which bulge has a greatest cross-sectional area thatis equal to at least 120% e.g., at least 180%, of a cross-sectional areaof a narrowest portion 246 of the caudal body portion caudal to thebulge (the caudal body portion may have an even narrower portion rostralto the bulge). Rostral and caudal bulges 234 and 234 help to prevent acurrent or a future type I endoleak at a rostral end and a caudal end ofan aortic aneurysm, respectively. Typically, when the stent-graftassumes the radially-expanded state, a site on rostral bulge 234 thathas the greatest cross-section area is within 10 cm of the rostral endof fluid flow guide 220, and a site on caudal bulge 244 that has thegreatest cross-section area is within 10 cm of the caudal end of fluidflow guide 220.

Typically, the stent-graft is configured such that bulges 234 and 244expand radially as the rostral end and caudal end of the aneurysmenlarge, respectively, in order to maintain a tight seal with the wallof the aorta, thereby preventing current or future type I endoleaks. Atthe same time, the stent-graft is configured to apply a radially-outwardforce that is sufficient to cause the bulges to expand with the aorticwall, but insufficient to itself cause expansion of the aortic wall. Forsome applications, structural members 214 and/or 216 are configured suchthat, when the stent-graft assumes the radially-expanded state, bulges234 and/or 244 each applies a radially-outward force that is less than aradially-outward force applied by anchoring elements 224. For example,the radially-outward force applied by each of the bulges may be between25% and 50% of the radially-outward force applied by the anchoringelements. For example, the anchoring elements may be configured to applymore than half a newton, no more than five newton, or between half anewton and five newton to the aortic wall. Rostral bulge 234 andanchoring elements 224 exert respective forces against the wall of theaorta, as described hereinabove regarding bulge 20 and anchoringelements 7, with reference to FIG. 4D.

For some applications, first and second subsets of structural stentelements 222 are configured to cause fluid flow guide 220 to definebulges 234 and/or 244, such as described hereinabove with reference toFIGS. 1 and 2, regarding bulge 20 of stent-graft 5. Stent-graft 200 mayimplement one or more of the described features of first and secondsubsets 22 and 23, which may have one or more of the describedproperties (e.g., spring coefficients).

For some applications, when the stent-graft assumes theradially-expanded state, rostral structural member 214 is shaped so asto define a generally cylindrical subportion 250 rostral to rostralbulge 234. For some applications, when the stent-graft assumes theradially-expanded state, rostral structural member 214 is shaped so asto define a generally cylindrical subportion 252 caudal to the rostralbulge. For some applications, a spring coefficient of rostral bulge 234,measured during application of a radial force by a rigid circular diskat a region centered at a first point of the rostral bulge that isfurthest from a central longitudinal axis of the stent-graft, is: (a) atleast 20% less than a spring coefficient of generally cylindricalsubportion 250, measured during application of the radial force by thedisk at a region centered at a second point of subportion 250 that isfurthest from the axis, (b) at least 20% less than a spring coefficientof generally cylindrical subportion 252, measured during application ofthe radial force by the disk at a region centered at a third point ofsubportion 252 that is furthest from the axis, and/or (c) at least 25%less than a spring coefficient of rostral anchoring elements 224,measured during application of the radial force by the disk at a regioncentered at a fourth point of the anchoring elements that is furthestfrom the axis, wherein the circular disk has a radius equal to 50% of aradius of the stent-graft at the first point.

For some applications, when the stent-graft assumes theradially-expanded state, caudal structural member 216 is shaped so as todefine a radially-outwardly flared subportion 260 caudal to caudal bulge244. For some applications, when the stent-graft assumes theradially-expanded state, caudal structural member 216 is shaped so as todefine a generally cylindrical subportion 262 rostral to caudal bulge244. For some applications, a spring coefficient of caudal bulge 244,measured during application of a radial force by a rigid circular diskat a region centered at a first point of the caudal bulge that isfurthest from a central longitudinal axis of the stent-graft, is: (a) atleast 25% less than a spring coefficient of flared subportion 260,measured during application of the radial force by the disk at a regioncentered at a second point of flared subportion 260 that is furthestfrom the axis, and/or (b) at least 20% less than a spring coefficient ofgenerally cylindrical subportion 262, measured during application of theradial force by the disk at a region centered at a third point ofsubportion 262 that is furthest from the axis, wherein the circular diskhas a radius equal to 50% of a radius of the stent-graft at the firstpoint. For some applications, a caudal end of the caudal structuralmember has a shape of a non-circular ellipse or a peanut shell shape(double-lobed) (which widens at each iliac artery, and narrows in themiddle).

For some applications, rostral body portion 210 and/or caudal bodyportion 212 comprise a plurality of anchoring elements 264 that extendradially outward, and assist with anchoring stent-graft 200 to theaortic wall. For some applications, the anchoring element comprisesbarbs, as shown in FIG. 13. The barbs of rostral body portion 210 may bedisposed on radially-converging portion 230, and may extend radiallyoutward in a rostral direction. The barbs of caudal body portion 212 maybe disposed on radially-diverging portion 240, and may extend radiallyoutward in a caudal direction. The barbs of the rostral body portion andthe barbs of the caudal body portion may thus extend in generallyopposite axial directions, in addition to extending radially outward.For other applications, anchoring elements 264 comprise tissueengagement members 52, described hereinabove with reference to FIGS.7A-C. For some applications, anchoring elements 264 of rostral bodyportion 210, which may comprise barbs, together with barbs 226 ofanchoring elements 224, which may extend radially outwardly andcaudally, together pinch tissue therebetween.

For some applications, stent-graft 200 comprises a plurality of barbs266 disposed at the caudal end of the stent-graft (as shown in FIG. 13)and/or at the rostral end of the stent-graft (not shown). Barbs 266typically extend radially outward and rostrally toward middle portion228 of the stent-graft. For some applications, stent-graft 200 comprisesboth barbs 266 and anchoring elements 264, described above. For someapplications, anchoring elements 264 of caudal body portion 212, whichmay comprise barbs, together with barbs 266, axially pinch tissuetherebetween.

FIGS. 14A-D are schematic illustrations of an exemplary method ofdeploying endovascular stent-graft 200 in an aneurysmatic abdominalaorta, using endovascular stent-graft delivery tool 4, describedhereinabove with reference to FIG. 4A, in accordance with an applicationof the present invention. In order to implant endovascular stent-graft200, the stent-graft is transvascularly (typically percutaneously)introduced into the aorta via one of iliac arteries 36, while thestent-graft is positioned in delivery catheter 30 in theradially-compressed state. Delivery catheter 30 and distal tip 31 ofdelivery tool 4 are advanced over guidewire 33 until the distal tip ispositioned slightly below renal arteries 32.

FIG. 14B shows rostral body portion 210 in an early stage of releasefrom delivery catheter 30. The rostral body portion is positioned nearrostral end 35 of aneurysm 34. For applications in which rostralanchoring element 224 are provided, the stent-graft is positioned suchthat the rostral anchoring elements are disposed rostrally to renalarteries 32.

FIG. 14C shows the stent-graft in a subsequent phase of its deploymentfrom delivery catheter 30, in which rostral bulge 234 is disposed inrostral end 35 of aneurysm 34, and sealingly contacts the aortic wall,thereby preventing or reducing the risk of a current or a future a typeI endoleak. Middle portion 228 has also been partially deployed from thedelivery catheter.

FIG. 14D shows the stent-graft in its fully deployed state, afterdelivery tool 4 has been removed from the subject's body. Caudal bulge244 of caudal portion 212 is disposed in a caudal end 270 of aorticaneurysm 34, and sealingly contacts the aortic wall, thereby preventingor reducing the risk of a current or a future a type I endoleak. Middleportion 228 has axially expanded as necessary such that the single lumenof the stent-graft entirely spans the abdominal aorta between renalarteries 32 and an aorto-iliac bifurcation.

FIGS. 14D-E show an optional portion of the implantation procedure, inwhich a bi-iliac self-expandable stent 280 is deployed in the iliacarteries, in order to facilitate improved long-term anchoring ofstent-graft 200 at the aorto-iliac bifurcation. FIG. 14D shows theintroduction of guidewire 33 or another endovascular guidewire, from anentry-point in iliac artery 36A to a contralateral iliac artery 36B.FIG. 14E shows the deployment of bi-iliac stent 280 over the guidewireinto both iliac arteries. Optionally, a balloon (e.g., an angioplastyballoon) may subsequently be inflated within the bi-iliac stent, so asto crush caudal flared subportion 260 of stent-graft 200 toward theaorto-iliac neck (not shown).

FIGS. 15A-C are schematic illustrations of stent-graft 200 coupled to auni-iliac self-expandable extension stent 300, in accordance withrespective applications of the present invention. A rostral end ofuni-iliac extension stent 300 is coupled to a caudal end of caudal bodyportion 212 of stent-graft 200 along a portion of a circumference of thecaudal end, such as less than 40 degrees of the circumference. Uni-iliacextension stent 300 is shaped such that a rostral portion thereofdefines a lateral opening 302 therethrough, defined by a discontinuityof stent cells along a portion of the circumference of the extensionstent, such as more than 320 degrees of the circumference. Afterdeployment of stent-graft 200 in the aorta and uni-iliac stent 300 inone of the iliac arteries, a bi-iliac stent (not shown) is advancedthrough the iliac artery in which uni-iliac stent 300 is positioned,passed through opening 302, and then into the other iliac artery. Thebi-iliac stent and uni-iliac stent 300 help hold stent-graft 200anchored in place, especially in the aorto-iliac bifurcation. For someapplications, the uni-iliac extension stent is bare, i.e., a fluid flowguide is not coupled to the extension stent.

For some applications, the bi-iliac stent comprises a super-elasticalloy, such as Nitinol. For some applications, a portion of theuni-iliac stent that is positioned in the other iliac artery comprisesan extension fluid flow guide, for treating an iliac aneurysm of theother iliac artery. The extension fluid flow guide comprises at leastone biologically-compatible substantially fluid-impervious flexiblesheet, and covers at least a portion of the uni-iliac extension stent.For some applications, the uni-iliac extension stent comprises asuper-elastic alloy, such as Nitinol. For some applications, at leastone radiopaque marker is provided for aiding in achieving a desiredrotational orientation of the stent-graft and the uni-iliac extensionstent. The at least one radiopaque marker is disposed on at least oneof: the stent-graft, the uni-iliac extension stent, and the deliverycatheter.

For some applications, as shown in FIG. 15B, a portion 304 of uni-iliacstent-graft 300 caudal to opening 302 comprises a fluid flow guide 306,which comprises at least one biologically-compatible substantiallyfluid-impervious flexible sheet, and which is coupled to a stent body ofthe uni-iliac stent-graft. The fluid flow guide may help treat an iliacaneurysm.

FIG. 15C is a schematic illustration of the configuration of stent-graft200 of FIG. 15B deployed in an aneurysmatic aorta, in accordance with anapplication of the present invention. Uni-iliac stent 300 is deployed inright iliac artery 32A. (The bi-iliac stent which is subsequentlydeployed is not shown in the figure.)

FIG. 16 is a schematic illustration of a configuration of stent-graft200 further comprising a plurality of circumferentially-disposed,axially-oriented engagement members 320, coupled to a caudal end ofcaudal structural member 216, in accordance with an application of thepresent invention. Engagement members 320 are configured to preventdown-migration of stent-graft 200 through the aorto-iliac bifurcation,which might obstruct the bifurcation.

For some applications, a self-expandable bi-iliac stent is furtherprovided (not shown). The bi-iliac stent comprises a bi-iliac stentbody, and, optionally, a fluid flow guide, which comprises at least onebiologically-compatible substantially fluid-impervious flexible sheet,and which is coupled to the bi-iliac stent body. The bi-iliac stent is(a) advanced through one of the iliac arteries, (b) passed throughengagement members 320, such that at least a portion of engagementmembers 320 and the bi-iliac stent-body engage each other (e.g.,interlock with each other), and then (c) into the other iliac artery.The bi-iliac stent helps hold stent-graft 200 anchored in place.

FIG. 17 is a schematic illustration of the configuration of stent-graft200 of FIG. 16 deployed in an aneurysmatic aorta, in accordance with anapplication of the present invention. The bi-iliac stent is not shown.

FIG. 18 is a schematic illustration of a configuration of stent-graft200 further comprising a self-expandable uni-iliac extension stent 340,in accordance with an application of the present invention. In thisconfiguration, a rostral end of uni-iliac extension stent 340 is coupledwithin caudal body portion 212 of stent-graft 200, typically at or neara caudal end of caudal bulge 244, such that the rostral end of uni-iliacextension stent 340 passes through the caudal end of caudal body portion212 and into an interior of the caudal body portion. Uni-iliac extensionstent 340 may help anchor stent-graft 200 in place in the aorta, as wellas treat an iliac aneurysm, in some applications. Stent-graft 200 andiliac extension stent 340 serve in combination as an aorto-uni-iliacstent-graft.

For some applications, a rostral portion 342 of the uni-iliac extensionstent is shaped so as to provide a lateral opening 344 therethrough,defined by a discontinuity of stent cells along a portion of thecircumference of the aorto-uni-iliac stent, such as more than 320degrees of the circumference. After deployment of stent-graft 200 in theaorta and uni-iliac extension stent 340 in one of the iliac arteries, abi-iliac stent (not shown) is advanced through the iliac artery in whichuni-iliac stent 340 is positioned, passed through opening 344, and theninto the other iliac artery. The bi-iliac stent and the aorto-uni-iliacstent help hold stent-graft 200 anchored in place.

For some applications, a caudal portion 346 of uni-iliac extension stent340 comprises a fluid flow guide 348, which comprises at least onebiologically-compatible substantially fluid-impervious flexible sheet,and which is coupled to a stent body of the uni-iliac stent. Fluid flowguide 348 may help treat an iliac aneurysm.

FIG. 19 is a schematic illustration of stent-graft 200 coupled to auni-iliac self-expandable stent 360, in accordance with an applicationof the present invention. A rostral end of uni-iliac stent 300 iscoupled to a caudal end of stent-graft 200. Uni-iliac stent 360 issimilar to uni-iliac stent 300, described hereinabove with reference toFIG. 15, except that a rostral portion of stent 360 does not lack anystent cells to particularly define a lateral opening therethrough.Instead, after deployment of stent-graft 200 in the aorta and uni-iliacstent 360 in one of the iliac arteries, a bi-iliac stent (not shown) isadvanced through the iliac artery in which uni-iliac stent 300 ispositioned, passed through one of the cells of stent 360, and then intothe other iliac artery. Because the passages through the cells aresmaller than opening 302 of stent 300, the bi-iliac stent in thisconfiguration must have a smaller cross-section when the uni-iliac stentassumes a radially-compressed state during delivery of the stent, thanin the configuration of FIG. 15. The bi-iliac stent and uni-iliac stent300 help hold stent-graft 200 anchored in place.

For some applications, a caudal portion of uni-iliac stent-graft 360comprises a fluid flow guide, which comprises at least onebiologically-compatible substantially fluid-impervious flexible sheet,and which is coupled to a stent body of the uni-iliac stent-graft. Thefluid flow guide may help treat an iliac aneurysm. Although not shown inFIG. 19, the fluid flow guide is similar to fluid flow guide 348,described hereinabove with reference to FIG. 18.

FIGS. 20A-21B are schematic illustrations of a configuration ofstent-graft 200 further comprising at least two (e.g., exactly two)iliac engagement members 400, in accordance with an application of thepresent invention. Iliac engagement members 400 are coupled to a caudalend of caudal structural member 216, typically on opposites sides of thecaudal end. Optionally, the engagement members are radially outwardlyflared in a caudal direction (configuration not shown). As shown inFIGS. 20B and 21B, a self-expandable bi-iliac stent 402 is furtherprovided. The bi-iliac stent comprises a bi-iliac stent body. For someapplications, the bi-iliac stent further comprises a fluid flow guide,which comprises at least one biologically-compatible substantiallyfluid-impervious flexible sheet, and which is coupled to the bi-iliacstent body (configuration not shown).

FIGS. 21A-B show two steps of an implantation procedure. FIG. 21A showsstent-graft 200 deployed in an aneurysmatic aorta, as describedhereinabove with reference to FIGS. 14A-D. Iliac engagement members 400extend caudally into iliac arteries 36. As shown in FIG. 21B, bi-iliacstent 402 is (a) advanced through one of the iliac arteries, (b) passedthrough iliac engagement members 400, such that engagement members 400and the bi-iliac stent-body engage each other (e.g., interlock with eachother), and then (c) into the other iliac artery. The bi-iliac stenthelps hold stent-graft 200 anchored in place.

In the present application, including in the claims, the term “rostral”means closer to the heart via the aortic vasculature, and the term“caudal” means further from the heart via the aortic vasculature. Forexample, the renal arteries are “rostral” to the aorto-iliacbifurcation. The terms “upstream” and “downstream” may be usedinterchangeably with the terms “rostral” and “caudal,” respectively, andrefer to the orientation of the apparatus with respect to the directionof blood flow.

Although the endovascular prostheses described herein are generallydescribed as being deployed via an iliac artery and the aorto-iliacbifurcation, for some applications, the prostheses are instead deployedvia a subclavian artery.

The scope of the present invention includes embodiments described in thefollowing applications, which are assigned to the assignee of thepresent application and are incorporated herein by reference. In anembodiment, techniques and apparatus described in one or more of thefollowing applications are combined with techniques and apparatusdescribed herein:

-   PCT Application PCT/IL2008/000287, filed Mar. 5, 2008, which    published as PCT Publication WO 2008/107885 to Shalev et al.-   U.S. application Ser. No. 12/529,936, which published as US Patent    Application Publication 2010/0063575 to Shalev et al.-   U.S. Provisional Application 60/892,885, filed Mar. 5, 2007-   U.S. Provisional Application 60/991,726, filed Dec. 2, 2007-   U.S. Provisional Application 61/219,758, filed Jun. 23, 2009-   U.S. Provisional Application 61/221,074, filed Jun. 28, 2009

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the present inventionincludes both combinations and subcombinations of the various featuresdescribed hereinabove, as well as variations and modifications thereofthat are not in the prior art, which would occur to persons skilled inthe art upon reading the foregoing description.

The invention claimed is:
 1. Apparatus for use with a delivery catheter,the apparatus comprising an endovascular sealing stent-graft, which isconfigured to initially be positioned in the delivery catheter in aradially-compressed state, and to assume a radially-expanded state uponbeing deployed from the delivery catheter, and which comprises: astructural member, which comprises a plurality of structural stentelements, and which, when the stent-graft assumes the radially-expandedstate, has a generally tubular shape, and is shaped so as to define atleast two elongated indentations, each of which (a) extends rostrally toa rostral end of the structural member, (b) is tapered in a caudaldirection until the indentation converges with the generally tubularshape of the structural member, (c) has an axial length of at least 2cm, and (d) defines a concave surface that is open to an exterior of thestent-graft along the entire axial length of the indention; and a fluidflow guide, which comprises at least one biologically-compatiblesubstantially fluid-impervious flexible sheet, and which is coupled toat least a portion of the structural member, and covers at least aportion of each of the elongated indentations.
 2. The apparatusaccording to claim 1, further comprising the delivery catheter.
 3. Theapparatus according to claim 1, wherein a rostral end of the fluid flowguide is disposed within 4 cm of the rostral end of the structuralmember.
 4. The apparatus according to claim 1, wherein a caudal end ofthe fluid flow guide is disposed within 2 cm of a caudal end of thestructural member.
 5. The apparatus according to claim 1, wherein thestent-graft further comprises a plurality of anchoring elements, whichare generally radially oriented when the stent-graft assumes theradially-expanded state.
 6. The apparatus according to claim 1, whereina rostral end of each of the elongated indentations spans an arc ofbetween 10 and 40 degrees, when the stent-graft assumes theradially-expanded state.
 7. The apparatus according to claim 1, wherein,when the stent-graft assumes the radially-expanded state, centers of twoof the elongated indentations are offset by an angle of between 70 and220 degrees, as measured with respect to a central longitudinal axis ofthe structural member.
 8. The apparatus according to claim 7, whereinthe angle is between 150 and 170 degrees.
 9. The apparatus according toclaim 1, wherein a diameter of the structural member is between 2.5 and3 cm, when the stent-graft assumes the radially-expanded state.
 10. Theapparatus according to claim 1, wherein an axial length of thestructural member is between 4 and 7 cm, when the stent-graft assumesthe radially-expanded state.
 11. The apparatus according to claim 1,wherein the axial length of each of the elongated indentations is nomore than 4 cm, when the stent-graft assumes the radially-expandedstate.
 12. The apparatus according to claim 1, wherein a rostral end ofeach of the elongated indentations is indented between 0.5 and 1 cm fromthe generally tubular shape of the structural member, when thestent-graft assumes the radially-expanded state.
 13. The apparatusaccording to claim 1, wherein the structural member comprises aself-expanding material.
 14. The apparatus according to claim 1, whereinthe structural member comprises a super-elastic alloy.
 15. The apparatusaccording to claim 14, wherein the super-elastic alloy comprisesNitinol.
 16. A method comprising: providing an endovascular sealingstent-graft, which is configured to assume a radially-compressed stateand a radially-expanded state, and which includes (a) a structuralmember, which includes a plurality of structural stent elements, andwhich, when the stent-graft assumes the radially-expanded state, has agenerally tubular shape, and is shaped so as to define at least twoelongated indentations, each of which (i) extends rostrally to a rostralend of the structural member, (ii) is tapered in a caudal directionuntil the indentation converges with the generally tubular shape of thestructural member, (iii) has an axial length of at least 2 cm, and (iv)defines a concave surface that is open to an exterior of the stent-graftalong the entire axial length of the indention, and (b) a fluid flowguide, which includes at least one biologically-compatible substantiallyfluid-impervious flexible sheet, and which is coupled to at least aportion of the structural member, and covers at least a portion of theelongated indentations; transvascularly introducing the stent-graft intoan aorta of a human subject, in a vicinity of renal arteries of thesubject, while the stent-graft is positioned in a delivery catheter inthe radially-compressed state; and transitioning the stent-graft to theradially-expanded state by deploying the stent-graft from the deliverycatheter in the aorta, such that two of the elongated indentations areradially aligned with the renal arteries, with rostral ends of theelongated indentations rostral to the renal arteries, respectively, andcaudal ends of the elongated indentations caudal to the renal arteries,respectively.
 17. The method according to claim 16, further comprisingidentifying the subject as suffering from an aortic aneurysm, whereinintroducing comprises transvascularly introducing the stent-graftresponsively to the step of identifying.
 18. The method according toclaim 16, wherein the stent-graft is one of a plurality of stent-graftshaving different, respective angles of offset between two of theelongated indentations, and wherein providing the stent-graft comprises:assessing an angle between the renal arteries; and selecting one of thestent-grafts having an angle of offset closest to the assessed anglebetween the renal arteries.